/sci/ - Science & Math

51

33.333%

49%

25%

≤50%

some very small difference between 49% and 50% everytime you satisfy a probability the other unsatified probability has a higher (0.000000000000000001) chance of occuring

i guess

>>981721
Hmm. There are two configurations possible, as far as I can see from mr. Smith's statement: 1 boy and 1 girl or 2 boys. This way, at least one of the children is a boy.... I don't see why it wouldn't be 50% chance :P

>>981721
i'm goin w/ 33% ..

bb
bg
gg

>>981743
imfukkenrite.jpeg

25%?

Protip: it's 50%

>>981743
how is gg an option...?
>I have two children and at least one of them is a boy.

My teacher told me its 33.3 but I still don't see how it isn't 50 percent. 50 percent still makes the most sense to me.

<span class="math">\mathbb{IT'S~FUCKING~50%~FAGGOTS.~JESUS FUCKING~CHRIST}[/spoiler]

It's 1/3

There are 4 possible scenarios before she says anything:
gg
bg
gb
bb

What she says eliminates gg, so we're left with:
bg
gb
bb

So there are 3 possibilities, and only one of them has 2 boys.

>>981750
>>981754

>>981754

It would be 33% if the question was 'I have two children, what is the probability that they are both male'. And it was defined in the question that the identity of each was irrelevant. In short probability sucks.

>>981757
you dumbfuck, gb = bg

>>981740

There are only 2 possibilities if you look at it that way, but one girl and one boy is twice as likely as two boys.

>>981753
in any case your options remain bb bg gg

"at least one is a boy" and "the other child is a boy" leaves you with 1 option plausable of 3 options available

>>981757
Why do you see a difference between bg and gb as there is no particular order?

>>981743
He's fukken' right.

There are three combinations of equally probable possibilities - BB, BG, GB. Only in one of these combinations are there two boys, so it's a 1/3 chance.

If Mr Smith had instead said "my oldest child is a boy", would the probability of the second child beinga boy change?

G G NOT OK
B G OK
G B OK
B B OK

3/4

Need more info, since the order of the child born will matter.
1st b 2nd g
1st b 2nd b
1st g 2nd b
1st g 2nd g <- Eliminated
So yeah 66% if the order matters.

>>981721
> Mr Smith says: "I have two children
♀♀
♀♂
♂♀
♂♂
> and at least one of them is a boy."
♀♂
♂♀
♂♂
> What is the probability that the other child is a boy?
1/3

>>981757
what you said would have made a difference if we were talking about which was born first.... but we're not
>facepalm.jpg

>>981768
yep 50% now

>>981763

Sure, you could combine them and say there are three possibilities: two girls, one of each or two boys, but in that case the probabilities aren't equal. You start with 2g (25%), 1g1b (50%) and 2b (25%)

If you eliminate 2g you get just 2b and 1g1b, but 1g1b is still twice as likely as 2b

>>981773
dumb
>>981772
dumb
>>981769
dumb
>>981757
dumb

>>981757
no because he said one of them is a boy so from

gg
gb
bg
bb
you are down to
bg
bb

gb gets thrown out too

>gb gets thrown out too
why?

you guys don't really understand probability. do you?

I hope everyone has figured out that GB and BG is the same thing.

>>981788
because the problem defines the first set as being boy, so gb has g in the first set, making it not possible. Now he didn't say which set was a boy, so i guess you could throw out bg instead. but either way one of them is thrown out.

It's 50%

I have two children - Possibilities:
BB
GG
BG

At least one of them is a boy - Possibilities
BB
BG

Why are you all under the notion that BG != GB. They're one and the same. He sets in stone that one of them is a boy so the other has a probability of being a girl or boy. 50%

TLDR; Mr Smith is a faggot

It's 1/3, everybody who says otherwise is a troll and/or idiot
Better question: What is the probability of at least 2 people having their birthday on the same day out of a group of 20?(disregarding leap years)

>>981800
haha, you are an idiot

>>981807
<50%

>>981763
wrong

>Mr Smith says: "I have two children and at least one of them is a boy." What is the probability that the other child is a boy?

>other child
not OLDER or YOUNGER child

we're looking for BB in a bag that contains GG, GB, BB.

33.3% chance.

75%

>>981789
We do, and the right answer of 1/3 has been given, along with explanations of why. But /sci/ is made of three competing forces. The second force is trolling and people intentionally giving the wrong answer. The third force is people who actually are stupid enough to think the answer is 1/2.

List of couple of child with 1/2 probality to be a boy:
first a boy, second a girl.
first a b, second a b.
first a g, second a g.
first a g, second a b.

One of them is at least a boy:
3/4

In the 3/4, proba the second is a boy:
3/4 x 1/3 = 1/4

respons: 1/4 = 0.25

only 3 fucking cases
1) 2 girls
2) 1 girl 1 boy
3) 2 boys

when 2 girls case is out the only 2 remaining are 1 girl 1 boy or 2 boys

so it's 50%
WAS THAT SO FUCKING HARD??
bg = gb DUHHHH

>>981824
see:
>>981814

>>981784
dumb

>>981777
Correct

Mr Smith tosses a coin and asks you to guess whether it's a head or tail. You decide to flip your own coin before answering; it comes up heads. Using an extension of the boy/girl logic, you reason that if there are two coins and yours is heads, there is only a 1/3 chance Mr Smith's is heads too, so you bet tails. Would this work?

Anyone who says it's not 1/3 should either get the fuck out or get banned for being underaged.

Suppose the contestants on a game show are given the choice of three doors: Behind one door is a car; behind the others, goats. After a contestant picks a door, the host, who knows what's behind all the doors, opens one of the unchosen doors, which reveals a goat. He then says to the contestant, "Do you want to switch to the other unopened door?" Is it to the contestant's advantage to make the switch?

>>981827
wtf?
are you canceling out an option?
let me borrow your logic for a moment .........

it can't be GG because we need at least one boy.
it can't be BG because we need one boy to have a brother.
SO,
the answer is 100% because the only option left is BB.

huuuuuurrrrrrrrrrrrrrrp

>>981841
Yes you're chances of winning increase from 1/3 to 1/2 now go away

i have in my underpants 2 balls and a penis if i say that what i am holding in my hand is my left ball what is the chance that in my other hand ill be holding my penis???
protip it's not 50%

>>981721


1/3

The possibilities are: Child A is a boy, Child B is a boy, they are both boys.

>>981833
no
duh...

>>981814
no no no, doesn't matter if he says other versus older or younger, plus you forgot about same age with twins.

Now, if he said "I have two children. you may define either as a boy. what are the chances both are boys?" you can say your 33.3%

>>981841

Of course not, that's ridiculous.

>>981833
no way man. no way.
this one's kinda common sense.

>>981833
nope, you only have information about your own coin, in girl/boy you have information about both

Congratz OP. You managed to troll /troll/.

>>981854
fukken troll

that's not what Mr. Smith said and you know it. english, motherfucker .......

>>981833
you are eliminating HH and one TH
HT and TT are the rest
50%

The prompt takes advantage of poor English to make the meaning/intent of the question ambiguous. By using the term other, you could have directly specified one of the children. In fact, if they are both boys then this would be the only logical conclusion. The most correct way to interpret it would be, as you asked directly later, stipifying that one of the children, older of younger was a boy then asking about the other. This creates a situation of two statistically independent events, wherein the probability is indeed 50%. It's not a matter of understanding probability. it is a matter of asking the question in a clear way. Better wording: A woman has two children. She has at least one son. What is the probability that she has two sons?

that a joke question?
he has 2 children - 1 is a known boy! so, its 50%, the other one can still only be girl or boy.

get a brian, morans

At start, 1/3 probability to win.

1 door is open.

You've then 1/2 to win.

I'll choose to open the other, cause of the better chance AT THE MOMENT...

That sounds weird btw:
As you see the game as a whole, whenever you choose to change or not, you'll have always 1/2.

>>981890
The original question is in no way ambiguous and you are a fucking idiot

>>981876
oh, i reread op, yeah it appears i am wrong. I was reading, one of them is a boy, not at least on of them.

>>981877
Yeah.

>>981890
Yes.

The coin-flip example is a fallacy

>>981897
Not 1/2, it's actually 2/3. If you increase the number of "dud" doors you can easily prove that it's always favourable to switch - since the gameshow host has perfect knowledge of which door the car is behind, and the car is never eliminated, the eliminations aren't random and the original odds stay for the whole group of doors.

>>981721

> Mr Smith says: "I have two children and at least one of them is a boy."

It is already mentioned that "at least" one of them is a boy. Thus it eliminate "two girls" from probability.

Thus:
1) boy + girl = girl + boy = 50%
2) boy + boy = 50%

Hence:
There is exactly 50% chance that it is either a boy or a girl. No science or logic can say that it is less or more than 50%.

When a randomly selected human male and randomly selected human female mate the product could either be a boy or a girl (if we do not consider hermaphrodite as third option).

>>981721

propably

How is it not, for all practical purposes, 50%?

>>981897
same OP here...

I've read something about the "perception of influencing" on probability.

A guy see another guy throwing a dice:
He will not bet on it.

This time, same guy throwing the same dice:
If asked, he could try a bet (just because of his "perception of influencing" the dice).

>>981934
Shit, hit submit instead of browse.

I meant to say, the coin-flip example is a fallacy as it specifies WHICH coin will be heads, which is mathematically equivalent to identifying Mr Smith's oldest child as a boy. It changes the odds in the same way to leave the heads/tails probability as 50/50.

This example was lifted wholesale from Martin Gardner's excellent book "Mathematical Puzzles and Diversions" (1959) which I compel you to read if you can.

>>981934
Ok, sounds legit ^.^

well, my main questions would be, where does he live, is he a native, is the child adopted and so forth.
without these pieces of information, I can only perform a thought experiment, which has no real correlation with reality.

>>981894
>the other one can still only be girl or boy
correct, but the question is:
>What is the probability that the other child is a boy?

>>981935
two girls is still in the bag.


see:>>981844
>we're looking for BB in a bag that contains GG, GB, BB.

I don't see in the statement where we are to assume the sex of the children are statistically dependent.

>>982015
you dont get it do you?
1 is 100% a boy (... at least one of them is a boy...)
1 is either boy or girl = 50%

q? what is the probability that the ___other child___ is a boy?
a: 50%

there is no such thing as a first or second child in the question.

>>982050
See:
>>981814

>>981935
Biology doesn't enter into it. Here's my MS paint explanation. We start off with four equally likely combinations, of which one is eliminated, leaving BB as a 1/3 probability.

>>982068
good job.

whydidn'tithinkofthat.mpeg

25 BROHA!

>>982068
the order does not matter.
boy + boy
boy + girl

its one boy, and one boy or girl, 50/50

i see the kids are home from school........
i'm out

>>982095
i don't think that's the order they are born. i think that's the possible outcomes.

The answer is "100% or 0%", the sex of the child is already determined

I believe order would only matter if they were not twins. so we do
not twins
bb
bg
gb
33.3333%
and twins
bb
bg
50%
then we multiply each by the percent chance of twins or not. then we add

so it's going to be about

35%

>>982095
in order to meet the criteria of at least one being a boy, you negate gg as an option. leaving you with 1 out of 3 options to answer the question

>>it's not 50%.

>>982120

>>982120
O.o - twin or not, its either boy or girl

also, boy + girl is the same as girl + boy
why? _one_ is a boy, not the first or second, one!

>>982144

>>982163

it's 49%

The fact that one is a boy doesn't matter at all.

OK I remember a probability thing like this before
It was about a Game Show
Door 1 has a goat, door 2 a car and door 3 some other shit
you want the car.
(some people like goats but for the sake of the problem the goal is the car)
When you pick a door one door is revealed
At this point you are given the option to change your pick.
they never reveal the car till the end.
You guys must have seen game shows like this before.
What is the probability that you get the car if you change your decision after one of the doors is revealed
Im telling you that it is something like 66.66666%
I don't remember why but there is a way to prove it.
In my high school class we did a quick experiment on it with pieces of paper and it actually did end up being that percentage after like 50 tries.

>>982120

>>981721
>>Mr Smith

i c wat u did thar

>>982095
>the order does not matter.
>boy + boy
>boy + girl

The question you're answering is "I have two children. One is a boy. What is the probability of the second child being a boy?" in which case OF COURSE it's independent and OF COURSE it's 50%. Same as if Mr Smith had seventeen children and wanted the odds of the middle child being a boy, or the heaviest child being a boy, or the one with glasses being a boy, or whatever.

The original question is subtly different, it's "I have two children and AT LEAST one of them is a boy. What's the probability that the other child is a boy?"

If I throw two coins and one lands heads, does that gives more or less chance that the other lands heads? Or tails?

One result does not affect the outcome of the other.

50% FTW.

OK
We have three options.
BB
BG
and GB
To all those people that say that GB and BG are the same thing you are correct.
BUT THAT POSSIBILITY OCCURS TWICE!
Essentially we have
BB and 2GB
It is 33.3333%
You are more likely to have a boy and a girl than have two boys.
Simple maths people.
(I think this is correct, I am not positive though.)

If you include BOTH BG as well as GB, then why not do the same thing for BB, such as B1B2 or B2B1?

This would then make all the possible outcomes:
BG
GB
BB
BB

Which would then make the probability of a second boy being 50%.
It makes no sense to switch GB for BG and not BB, since that may be the case. But BB = BB, therefore GB = BG, because there is only one order in which they are born. The fact of the matter is that it is not specified, therefore you can go with EITHER GB or BG, not both, otherwise you'd have to do it to GB. What you do to one side you must do to the other.

Conclusion: It's 50%, not 33% because of algebraic rules.

>>982175
Yeah, always change your choice if you're given the option.

Reminds me of somethin that goes:
I have two envelopes with cash in them. One envelope has twice the amount of cash as the other (so the other has half as much). I give you the option to choose an envelope and you can have the cash inside it. Once you choose, and before I give it to you, I give you the option to switch. In this experiment there is no benefit of swapping. on average

>>982214
otherwise you'd have to do it to BB*

>>981721

25%

>>982189
This. To clear up you would need to rephrase the question:
>What's the probability that Mr Smith has two boys?
It's subtle difference. No wonder no one who didn't lnow this problem beforehand got thrown off.

>>982189
This. To clear up you would need to rephrase the question:
>What's the probability that Mr Smith has two boys?
It's a subtle difference. No wonder everyone who didn't know this problem beforehand got thrown off.

>>982222

Sorry no. I forgot the one is surely boy.

Therefore it's 50%

>>982214
agreed with this

>>982189
at least:
1 boy or 2 boys, but _minimum_ 1

leaves the possibilities:
1 boy + 1 boy
1 boy + 1 girl

we can argue about biology - there are slightly more males being born.

why are people still arguing about this, this is simple:
we already know the first child is 100% a boy, leaving the second child.

the only choices we have are 50% boy and 50% girl.

how do you get 33%? or anything else for that matter?

taking into account we don't apply transgender or the actual chances of male or female conception.

>>982239
>>982240

wtf? No you don't use other data than that given in the OP!

50-100%

again........

Two children - combinations are BB, BG, GB, GG

At least one child being male - combinations are BB, BG, GB
Probability of both children being male - 1/3rd, or, 33.3%

>>982212
I'm leaning towards this explanation.

>>982252
what other data?
one is a 100% boy, the other is either boy or girl. order was not asked. and we humans only have two genders.

>I have two children and at least one of them is a boy
GG
GB <-
BG <-
BB <-
at least one = 1/3
BUT
>What is the probability that the other child is a boy?
>other child
GB
BB
50%
You guys are fucking retarded

>>982264
If order matters, then it would be B1B2, B2B1, GB, BG, in which case the probability of both children being boys is 50%.

eat.
http://www.bbc.co.uk/dna/h2g2/A19142246

You are all thinking Math.
Because of those stupid fags I went to law school.
It's all about how people word their questions.
First off, OP didn't give us any facts. He just said what Mr. Smith said. For all we know he could be lying and have no children, or two girls, or three, or whatever.
But assuming Smith is being truthful, then he has two children and one is a boy.
The question is: What probability of gender male is the remaining Smith child?
Considering there are two possible options and assuming all possibilities are equaly distributed, then 50%.
If you want to propose a stupid challenge, learn how you word your question properly.

>>982240
>First child 100% a boy.
It does not say that.
That is an incorrect assumption that you have made.

12.5% male - straight
12.5% male - gay
12.5% female - straight
12.5% female - gay

>>982214
>>982221
>>982239
>>982240
>>982276
>>982278
>>982285

/thread.

>>982293
You're missing an entire range of paraphilias.
Like pedo, ephebophile, omniphile, assexual, any-fucking-word-you-can-think-of-phile.

>>982264
GB and BG are the exact same thing, so no, it is 50%

>>982276
oops i meant 3/4 not 1/3

>>982292

ONE child is a boy, order does not matter. go nitpick some other detail because you know you've been proven wrong and have fail logic.

Well we have surely learned one thing, /sci/ does not understand probability

Probability - the new way to troll /sci/

>>>>>Now let us look at the second question, which states that at least one of the children is a boy. This means that out of the four possibilities, only GG is impossible owing to the fact that it does not contain a boy. As the second question does not state whether the boy is the older or the younger child, it is possible to have any one of GB, BG or BB. In other words, the boy we know of could have an older sister, a younger sister or a brother1.

Note that the last possibility, BB, should only be counted once. This point can be confusing and thus merits a further explaination. First, let us look at GB and BG:

* GB = there is a younger boy who has an older sister.
* BG = there is an older boy who has a younger sister.

Clearly, these two situations are different, and thus represent two distinct possibilities. However, let us treat the ways in which BB might occur in the same manner:

* BB = there is a younger boy who has an older brother.
* BB = there is an older boy who has a younger brother.

Unlike the first pair of sentences, the ones for BB both describe the same situation - the words we use to describe BB simply depends on which of the boys we think the question has already referred to. BB is therefore only one possibility out of three, and thus has a 1⁄3 probability of occurring. On the other hand, having an older boy and a younger girl is different to having an older girl and a younger boy, and the probability of the family including a girl is therefore 2⁄3.

* Two children → combinations are BB, BG, GB, GG.
* At least one child is a boy → combinations are BB, BG, GB.
* Probability of one child being a girl is 2⁄3.

The problem we have in this threas is that we have a bunch of kids or high school drop outs that did not study probability properly.

OK I will try my best to explain why it is 33.3333%
Because That is the correct answer.
Simple logic says that it is not.
But Simple Logic is not correct in this question.
Let us first look at the problem.

Mr Smith says: "I have two children and at least one of them is a boy." What is the probability that the other child is a boy?
Now if Mr. Smith comes up to me and says this to me I know nothing of the order in which the children were born. All I Know is that one of them is a boy.
There are 3 possibilities.
A girl was born first and then a boy
A boy was born first and then a girl.
A boy was born first and then another boy was born.
Each of these has an equal chance of happening.
But there are two instances in which a girl is born.
Only one in which a girl is not born.
Now I am pretty damn certain this is correct. I have done problems like this a lot (Mainly last year) and consider myself to be good at them.
If someone has a legitimate proof as to why this is not correct I am happy to debate it.

>>982292
yes, it does. on child is absolutly 100% surely a male.
what is the other one? boy or girl?

pay attention here..

>Clearly, these two situations are different [BG,GB] and thus represent two distinct possibilities

>>981721

From the OP

>two children
>at least one of them
>other child

Boy - Girl is IDENTICAL to Girl - Boy
It's till 1 Boy and 1 Girl. Which child is of which sex is IRRELEVANT CAUSE IT'S NOT SPECIFIED IN THE OP.

STOP TROLLING

IT's OVER 9000/18000!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

and >Probability of one child being a girl is 2⁄3.

meaning: the probability of one child being a boy is, in fact, 1/3.

JUST EVERYBODY LISTEN THE FUCK UP.

IF ORDER MATTERED, THEN ALL THE POSSIBLE POSSIBILITIES WOULD INCLUDE

GG
GG
GB
BG
BB
BB

MR.SMITH HAS AT LEAST ONE CHILD WHO IS A BOY, THEREFORE WE ARE LEFT WITH

GB
BG
BB
BB

IF ORDER DID IN FACT MATTER, THEN THE PROBABILITY OF THERE BEING TWO BOYS WOULD BE 50%.

IF ORDER WAS NOT A FACTOR, THEN

BB
BG

IN WHICH CASE, THE PROBABILITY OF THERE BEING TWO BOYS IS STILL 50%.

THERE ARE TWO GENDERS: BOY AND GIRL.
NOT THREE, YOU IDORTS. SO GET THE 1/3 SHIT OUT OF YOUR HEAD AND STOP TRYING TO SEEM LOGICAL.

>i am 12 and think gb = bg

they're separate scenarios with equal probabilities to bb; 1/3.

fucken b&s and trolls

>>982337
What if they're twins?

2/3

>>982337

>implying the order in which they are born is relevant
>implying the OP did ever ask for it
>implying the is something like complex logic

>>982344
>>982349
see:
>>982283

Protip: Nobody here is taking into count variable change...
l2math.
There is a 1/4 probability for each to occur:
bg
bb
gg
gb
For you idiots who think bg and gb are the same, SDF972J3F8923JF SHUT UP YOU'RE STUPID.
Back to the math
gg is eliminated, leaving us:
bb
bg
gb
The probability is 33%.

the answer is 2/3

>>982344

This!

Work with what is given in the OP. Which of the two is the male is irrelevant!

God damnit, it's 50%, you're getting trolled there

>>982372
yes.
now go finish your homework

>>982349

jesus christ, are people stupid.

mr smith says: "i have two children and at least one of them is a boy." -----> one is a boy
what is the probability that the other child is a boy?

one is already a boy, what can the other be? a boy or a girl?

(hint, he cant be a girlboy)

Seriously, he has a boy, that information is extra and not relevant. The question is whether his other child is a boy or not.
Boy = 50%
Girl = 50%
>Protip: it's not 50%
OP is a troll and/or moron.

>>982349
I repeat my coin-toss argument.
I throw two coins. One lands heads.
The other may have landed before or after this one.
Does the I-know-it-was-Head Coin affect the outcome of the other? If so, could you please explain me why?

P.S.: They didn't collide in mid-air.

ARE YOU TRYING TO TELL ME THERE IS A 33% CHANCE OF A GIRL, 33% CHANCE OF A GUY AND 33% CHANCE OF A GUY?

ITS 50% HOLY SHIT I MAD

the answer is 2/3 because...

if one child is a boy then either he has bg or bb.

if he has bg then there is only one way he can choose the boy. but if he has bb, there are two ways.

so there is a 2/3 chance that he has bb.

>>982353
this

>>982278

>If order matters, then it would be B1B2, B2B1, GB, BG, in which case the probability of both children being boys is 50%.
>B1B2, B2B1

How on earth can you have the second son being born before the first son?

The first child was either a boy or a girl. The second child was either a boy or a girl. Look at the grid; that makes FOUR equally likely combinations. Now we remove GG because we're told one child is a boy. That leaves us with three equally likely combinations (BG or GB or BB). Don't get hung up on the fact that there are only two possible OUTCOMES (two boys or a mix) because one of those outcomes is more probable.

Think of it this way. If you play the lottery, you either win the jackpot or you don't. There are only two possible outcomes. But this doesn't mean that every time you play the lottery, you have a 50% chance of winning the jackpot.

tl;dr: look at the damn grid.

Probability this thread is being Trolled:
99,7%

50% of people are men and 50% of people are women, it's 50%

the question is: what is the probability that one child is a boy?

two issues:

girl, boy

1/2.

>>982389
That's way too optmistic...
I'd say at least 110%.

>>982385
oh. my. fucking. christ.

no.

but the PROBABILITY THAT THE OTHER CHILD IS A BOY is 1/3.

not saying that the sex of the child will change or any dumb fucking douche bag mad prop shit your dribbling from your chin.

look the fuck down, you're standing in a puddle

>>982366
Thank you so much.
The first person in this thread to do the implication shit and it is for the wrong facts.
What I am seeing in this thread is two groups.

People that actually belong on this board and people that are going onto this board while browsing other boards.
Some people in this thread are over 20.
Others are well under 15.
This kind of probability question is High School probability, not Year 7 stuff we are talking Year 11 and Year 12.
Age does not always mean you are smarter, I am quite happy to admit that but this thread is proving it to be otherwise.
In probability order is ALWAYS relevant.
In probability order is ALWAYS relevant.
In probability order is ALWAYS relevant.
I typed that three times to help you remember it for later use in life.
In probability order is ALWAYS relevant.

>>982332
* BB = there is a younger boy who has an older brother.
* BB = there is an older boy who has a younger brother.

This part is basically right, but what you said later on is wrong. You have to assume both, because they are not, in fact the exact same thing. There are two different people and the ages of both become a factor if we assume all of what you said is right, bar the part I quoted. Basically, you can't rule out a second BB.

>>982383

Is one of the 2 coins made of magnets?

>>982383

>flip a coin, know state of one known coin
>know one is a boy, know the state of one unspecified child

>>982402
Both. also, throws made near magnetic north pole.

you dumb asses that are saying 50% need a fucking book to read.


I have one child, what is the probability that it is male?
====50%

i have two children, one is male, what is the probability that the other is male?
i'm12andwhatisthis.jpeg

we are logic:
one child is a known boy
the other can only be girl or boy - 50% chance

lower your stupidity and learn math, resistance is futile

>>982404

I'm >>982383

I'm sorry, are you agreeing with me or trying to explain the difference between the coin toss and Mr.Smith child's scenario?

>>982410
>you dumb asses that are saying 50% need a fucking book to read.
>I have one child, what is the probability that it is male?
>====50%
.......did you just disagree with yourself and call yourself a retard?

Right now I can guarantee that There are kiddies raging at their computers about people saying it is 33.3333% and not being able to comprehend it.
We will also have older people flipping out over the fact that kiddies can't get past that fact and the kids keep saying it is 50% because that is all that makes sense to them without further education.

Then we have the trolls who are laughing all the way to the bank.

>>982435
or "dumb ass" rather

I think the problem will be clearer if I restate it a bit:

Mr Smith says: "I have two children, and they are not both girls". What is the probability that Mr Smith has two sons?

In this case the probability is clearly 1/3, as has been proven several times in this thread.

Now, some people confuse this with the similar sounding question "If the first child is male, what is the probability that the second is male?". Although this sounds similar it is in fact a completely different question and it that case it would be 1/2.

>>982435

That 50% was for a different question.

Oh god. /sci/ is either full of trolls or dumb as hell.
The probability is 50%.
You don't even need to care about the child that you know is a boy.
Since it's already determined, now you need to focus that the other one is either a Boy or a girl.
Assuming a perfect situation (absolutely randomly determined disregarding the physical and biological factors), the chance is 50%, because there are two variables and neither outcome is favoured by any factor.
The only possible outcomes are either BB or BG.

>>982435
uhm, no. thnx tho

lrn2read

>I have one child, what is the probability that it is male?
>I have one child
>one child
>one

vs.

>i have two children, one is male, what is the probability that the other is male?
>i have two children
>two children
>two

i recant. the answer is 1/3

>>982440
>Mr Smith says: "I have two children, and they are not both girls". What is the probability that Mr Smith has two sons?

>In this case the probability is clearly 1/3, as has been proven several times in this thread.

Both not girls? Then they have to be boys, so the probability they are male is 100%.

>Boy or Girl paradox
Google it.

>>982440
The original statement, clear for all to see in the original post, is "I have two children and at least one of them is a boy." So that leaves only one child undetermined. The options are boy and girl. Only two choices with each being just as likely. 50% is the answer.

The 1/3 answer requires options that the original statement precludes.

>>982453
so the probability of another child being male all of a sudden changes? This thread is full of retards....

>>982349 >>982344 >>982313 >>982306
>>982304 >>982298 >>982285 >>982278
>>982276 >>982274 >>982255 >>982240
>>982234 >>982233 >>982222 >>982214
>>982210 >>982161 >>982144 >>982095
>>982094 >>982050 >>982015 >>981938
>>981935 >>981914 >>981897 >>981877
>>981859 >>981854 >>981852 >>981827
>>981824 >>981815 >>981812 >>981801
>>981800 >>981799 >>981788 >>981785
>>981784 >>981775 >>981772 >>981769
>>981767 >>981763 >>981750 >>981748
>>981740 >>981738 >>981733 >>981732
>>981726 >>982421 >>982402 >>982400
>>982393 >>982386 >>982385 >>982382
>>982381 >>982377 >>982374 >>982372
>>982366 >>982365 >>982448 >>982410

sure is troll and retard in here

>>982448
In probability Order matters.
The guy that posted before you mentioned that this is not saying the First child is Male.
If that was the case, Which most people are taking as a given in this thread 50% would be correct.
This is not a given and should not be assumed as a fact.

In probability the order matters.
The other assumptions in this thread are that twins were not born which given the circumstances is a logical assumption.

The only combiniation of two children that is not allowed is two girls. So, either it is boy and girl, boy and boy or girl and boy.

So... it is 1/3 that the "other" child is a boy.

>>982466
Yes, both accounts.

you no longer have B and G as outcomes.
you have BB, BG, GB, GG as outcomes.

>>982463

"Both not-girls" and "not (both girls)" are two different things.

"I have two children, and it is not the case that I have two daughters." if that is less confusing.

two children, at least one is a boy. what is the other one? - girl, boy or mutant? = 1/3

trollface

What is the probability of the sun rising in the morning?

* Rise
* Don't rise

Therefore, 50%.

>>982471
Exactly. Once that first child is born, the probability changes. Probability is fluid and changes as new information and new things come about.

>>982482
no, you don't have GB and GG because we know the first one is a boy. There for you are left with BB and BG.

>>982470
tl;dr

>>982471

So what if order matters?
If you had a machine that chose one of two elements completely randomly, their results would still be independent.

2/3

Girl Girl - 1/3
Boy Girl -1/3
Boy Boy -1/3

At least one is boy
1/3+1/3 = 2/3

>>982471
>In probability Order matters.
ohyou.jpg

>>982503
lrn2read

>"I have two children and at least one of them is a boy."
>at least one
not
>the first one

If Order matters, then please, I'm not trollin, I just want to understand it...

What happens in my coin-toss scenario?
I throw two coins. One of them lands heads. Maybe the first to land or the second.
Does that affect the outcome of the other friggin coin? If so, how and why?

Please... .. .

>>982510
>Implying order doesn't matter.

1/3

>>982515
Btw, if this is different from Mr.Smith's children, then please explain my why, too...

>>981721

OP is probably a fag

Given the question that was asked, and accounting for all reasonable possibilities, the correct answer is 1/3.

>>982517
>implying it is an absolute.

What is the probability of rolling a 6 with a dice?

When rolling a dice, there are two outcomes: the top face is 1, or the top face is greater than one. Since there are two outcomes, they each have probability 1/2. Therefore the probability of rolling a 6 is 50%.

checkmate trolls

GB and BG are the same thing. Therefore your options are BB and BG/GB. 50%, not fucking 33%. Am I getting seriously trolled, or is this thread just full of idiots?

To all the kids in this thread.
I encourage you to take this problem to your teachers today.
Make sure that you copy it word for word because the wording is crucial to the answer.

Now regardless if you believe me or not I am telling you that the answer is 33.333333%.
If I was your age I probably would not believe me.
Just take it to your teacher and see what they say.
If they are a maths teacher and instantly say 50% they are a shit teacher. (Because no maths teacher should answer a problem without actual thought to it.)
Trust me on this guys.

>>982537
You're trying way too hard, and unfortunately, your succeeding.

>>982515
doesn't change the outcome of the toss. but if you're looking for a certain outcome of both tosses then the probability will change.
same applies to mr. smith's trolls

http://en.wikipedia.org/wiki/Boy_or_Girl_paradox
Knock yourselves out.

>>982515
probability is based not on the situation but also on your KNOWLEDGE of the situation.

In the coin tosses, say one is heads, what's the probability the other is heads? The outcomes are:
HH
HT
TH
each of these is of equal probability to each other, so the answer is 1/3

>>982515

I'll bite. What is the probability that in two coin tosses you'll get two heads, if you know that if the first toss was tails, the other can't be tails also?

>>982537
>>982537

there is no thinking... "at least one is a boy" = ONE IS A BOY, at this point you must determine the gender of the other, it can be a boy or girl, there is however poor mastery of the English language

one is known, the other is unknown, can be girl or boy - 50%

>>982543
>your

>>982546
GODDAMMIT WHAT IS WRONG WITH YOU. HT is the same as TH. If we know that one is heads, and one is tails, then obviously the other one is the T, regardless of which one you put first.

>>982552
to answer the question BOTH MUST BE BOYS!!!

>>982544
>>982546

So, my knowledge of te outcome of first coin changes the outcome of the second?

I can gamble with this and rip money of all fucktards who bet with 50%, cause I'll win 66%? Is this right? Can I trust you, anon? For real? I'll be rich and donate some to y'all.

>>982531
I lol'd

>>982545
that's a good article.... i edited it myself.

>GB=BG

Come on, that's like saying probability of the sum of two dicerolls being 7 is the same as probability of it being 2.

>>982545
no - the questions in the article are different:
* Mr. Jones has two children. The __older__ child is a girl. What is the probability that __both__ children are girls?
* Mr. Smith has two children. At least one of them is a boy. What is the probability that ___both___ children are boys?

marked the different parts

>>982458
Googled the paradox and I have determined that professor Martin Gardner is an idiot. But I jest. He is good at math but sucks at english. He doesn't know that "at least one of them" is not a vague statement, but a very specific statement that "definitely one of them is" in fact a boy. His statement contradicts his meaning. This isn't a paradox, it's a damn mistake on the part of the originator.

>>982560
dude, listen. it doesn't change the outcome of the next coin toss/child. you still have H or T / B or G

but to meet the requirements of the question you need certain results/outcomes. these results is what the probability is.

and, yes, you can always trust anon.

>>982557
no, ht =/= th. if it helps you understand better, imagine one is red and one is blue (this won't change any probabilities, of course)

>>982560
almost. your partial knowledge of the entire state of the system (one of them is heads) necessitates you update probabilities accordingly. you don't know which one is heads, though.

and yes, people have gotten rich off of this fact. see: Deal or No Deal.

>>982574
We already know that one is a boy, which means there will be one B no matter what. Putting it after the G instead of before it doesn't change anything! IT'S THE SAME THING.

>>982575
wtf... derp

in your question is one of the kids multiple-personality?

>the other child is a boy
implies
>both children are boys

>>982585
You just don't fucking get it do you?
see:
>>982588

>>982560
>So, my knowledge of te outcome of first coin changes the outcome of the second?

You don't have any knowledge of the outcome of the FIRST coin flip in particular. That's an essential part of the problem. You only know that at least one of two flips was H, and both flips have already occurred.

>>982595
the kids aren't twins. older sister =/= younger sister

I want to participate, but damn, tldr guys

>>982600
I said first as in 'first one I know the outcome'

Why wouldn't bg and gb be commutative?

Does the girl's gender magically change if she is placed in a different spot from where the boy is standing? Does the boy suddenly change gender as well? No? Then what's the difference between the two? We're not asking who is younger or older, we're asking what the odds are that this second child is a boy or a girl

>>982603
older/younger/twin/left/right/purple does not matter.
1 is a boy, what is the other? boy or girl?

>>982609
Just say 1/3 or 1/2 or 33% or 50% or any made up number and curse everyone else... no need to read all the long posts.

>>982588

I must admit I worded that post badly. But assuming random genders GB combination is twice as likely as BB combination - it happens in two cases, while BB happens in one.

One of the boys could be a girl.

>>982622

This is the last way I can possibly think to explain why it GB and BG are the same thing, then I'm gonna go punch something.
Since we know that one of his children is a boy, in both GB and BG, the boy that we already know of has to be "B". Therefore both GB and BG are saying that the unknown child is a girl, regardless of order. If you guys are trolling me, it's fucking working. Somehow I get the feeling you're not though.

>>982611

in some respects. they are the same. but you have to remember that with sets of two completely random children, the combination "one boy and one girl" occurs twice as often as the combination "two boys". that's a fact, regardless of how you label things.

>>982626


This is impossible, penis overrides tits. Always.

>>982613
>implying having older sister (say 18yo) = having younger sister (say 12yo)
>implying 18 = 12

>>982637
they're not both random though! We already know that one is a boy!

you all went to public school didnt you?

>>982555
is right

25%
he can there are 4 outcomes
bb bg gg gb

>>982646
Finally someone else who agrees with me. Thank you.

Outcomes:

BB
BG
GB
GG

We know one guy (X) is a boy, so X = B
leaving:

XB
BX
XG
GX

the other one can be either:
the second child, a boy.
the first child, a boy.
the second child, a girl.
the first child, a girl.

2 out of 4 of being a girl.

>>981721
>Mr Smith says: "I have two children and at least one of them is a boy." What is the probability that the other child is a boy?

So we've got:
BG
GB
BB

However, it says that the *other* is a boy, too, so we're looking from the boy's perspective. In which case the above turns into:
BG
BG
BB

But the first and second are the same now, so it becomes:
BG
BB

50%

>>982648

>>982613
that's not the question...

>what is the probability that the other child is a boy.
>implying that both children are boys

>>982646
>private school
>better than public school

Oh, America, why does everything have to be the wrong way around over there?

>>982654

Two wrongs don't make a right.You are still wrong.

>>982656
>230 posts omitted
>a simple concise response

/sci/ sure r good at probability

>>981721
>>982545
>http://en.wikipedia.org/wiki/Boy_or_Girl_paradox
>Many people, including professors of mathematics, argued strongly for both sides with a great deal of confidence, sometimes showing disdain for those who took the opposing view.

OP used God-tier Troll.
It's Super-Effective

>>982642
if you know specifically that one is a boy, then why can't you answer either of these questions with 100% confidence?

"I have two kids, Jan and Casey. At least one is a boy."

1. Is Casey a boy?
2. Is Jan a boy?

If you actually knew anything about any specific child, you would be able to answer one of those questions with absolute certainty. But you don't.

>>982665
it answers the question - boy or girl? 50/50
50%

You guys are spinning in circles.
If someone hasn't gotten it by the 250th post,
the odds are they won't at all.

>>982642
that doesn't change the fact p(gb or bg) = 2 p(bb), hence making bb 1/3

>>982676

its only a god teir troll because there aren't enough mathematicians that understand goddamn english, because americans and the english are retarded

>>982676
its not the girl/boy paradoxon, those questions are slightly different than the op. read carefully.

>>982679

casey sounds like a fag boy name
jan is the girl

1. One child is a boy.
2. Other child can be either boy or girl.
3. The boy can be younger or older than his sibling.
4. Mr. Smith can be nigga or white.
5. Hell, he can even be latino or asian!
6. I can be a troll or not.
7. OP can be a troll or just plain stupid.

So, considering the only relevant info is #2, that leaves us with 50%, right?
Also, 7 may be relevant, but somehow doesn't affect the probabilities:
BT
BS
GT
GS
TB
TG
SB
SG

where B is boy, G is girl, T is OP is trollin, S is OP is stupid.
50-50 for B and G

"I flipped two coins, and at least one was heads. What are the chances that I got two heads?"

25% Only correct answer to this question.

It doesn't matter that Mr Smith has 2 children.
Remove the boy and we have to guess the gender of 1 child.

Boy or Girl. 50%.

You guys are making this harder than it is.

>>982738

It's 1/3. We know you didn't get two tails.

>>982738
What are the other 75%?
25% heads tails,
25% tails heads,
and 25% tails tails? But what happened to the one that was heads?

Mr Smith says: "I have two children and at least one of them is a boy." What is the probability that his wife cheated on him?

>>982738
i'd gladly bet funds against you on that one

people fail logic, just the second child is asked. chance of beeing a boy? boy or girl - 50%

<- This thread.

this thread makes me shamed of /sci/.
l2stochastics!

Wow. Just wow. I honestly didn't intend for this to become such a huge shitstorm.

I actually tallied up the number of correct/incorrect posts and about 60% of people are wrong - either by applying incorrect logic or by assuming it's 50%.

Let me try to shed some light onto what most people seem to be getting hung up on: the fact that there are two OUTCOMES given not-GG: BB or a mix. However two OUTCOMES doesn't mean an equal two-way split in terms of probability, any more than "the sun will rise or not rise, therefore it's a 50% probability" is true.

To people who think that BG and GB are the same thing: ever heard of Pascal's Triangle? Not all outcomes have equal weighting as some combinations are more likely. Pic related. Get rid of the female-female bar (as that's given in the question) and you can see it's not male-male isn't as likely as a mix. BG and BG are not order-specific and so we count permutations, not combinations.

>>982676
this

>>982739

You are saying it like what we do here is hard.

Don't worry, just because you don't understand, it doesn't mean it's wrong.

ITT we attempt to make up for 2nd grade literacy with Bayesian probability

>>981768
>implying that from the beginning the chance of boy/girl was 50%
There are statistics that show that more men than women are born because in ancient time the men (hunter) died oftener.

Okay, let's just assume for the sake of argument of the unknown child is a boy...
So...
100%

/thread.

>>982766

You guys are making random probabilities, there is NO WAY the known child has any effect on the unknowns child's gender.
There is no reason for them to be noted together.

>>982763
is not the boy/girl paradox - the question is (slightly) different.

paradox: asks the chance of both kids beeing the same gender.

op: asks the chance of one child beeing a boy

>Mr Smith says: "I have two children and at least one of them is a boy."
Disregard that...

>What is the probability that the other child is a boy?
>What is the probability that child is a boy?
Assuming any child has 50:50 of being boy:girl, then 50%.

>Protip: it's not 50%.
...I suck COCKS!

OP, lrn2english

>>982811
Thus,
>OP used God-tier Troll.

>>982836
agreed, op should go into politics, hes good

>>982799
>for the sake of argument
>/thread.

OP is good, but God-Tier?
I've seen a few better trolls in the old days, when /b/ was good.

For all you people who think bg=gb, go to a dictionary and look at the definition of combination. Now look at the definition of permutation. In this case, the probability is based on a combination, because he says one is a boy, but doesn't specify which one, SO ORDER MATTERS! It's like that one riddle that says 2 coins equal 10 cents and one isn't a nickel, so what's the other?

>>982849
I'm unfamiliar with said riddle, could you state it fully, please?
Also, not amerifag, so nickel is what? 5¢?

>2 coins equal 10 cents and one isn't a nickel, so what's the other?

yeah, its something like that

>>982849
see
>>982830
/thread, glorious god tier trolling

>>982849
But it's not like that at all. That is what the originator of this problem eventually admitted he meant, but he sucks at english.

Next, we go to /po/ ask what kind paper is good.

>>982861
yeah, nickel is worth 5 cents. The riddle says you have 2 coins that add up to 10 cents, and one of them isn't a nickel. There is no way to get 10 cents from 2 coins without having a nickel, so you say to yourself, "ok, one of the coins isn't a nickel, but there has to be a nickel in there somewhere, so the OTHER coin has to be a nickel." Probability is quite tricky.

bg =gb. Order doen't matter.

However, bg is twice as much more probable to occur than gg or bb.

>>982930

yeah, only the other one is a nickel, the other one is a 5 cent penny

The question isn't
"What is the probability that both children are boys?"
it is
"What is the probability that the other child is a boy?"
The actual asked question is about the other child, not about both children. Therefore, it's boy or girl. 50%
The prior information is irrelevant in this case.

>>982957
truth

/thread - let it die

>>982957
This, you people are fucking idiots. The answer is 50%

>>982945
>5 cent penny
aka: nickel

>>982907
truth

/thread - let it die

>>981721
pic not related

I don't think that every one here is taking into account that regardless of how many previous children they have and considering that we don't have any other information to indicate that they aren't a healthy couple, the odds show us that there are four separate possibilities two of which are the egg and sperm becoming a girl and the other two becoming a boy, therefor the odds are that there is a 50:50 chance of them having a boy to a girl.... right? Or am I forgetting something?

>the other child is a boy?

in this case, it's 1/2. The OP identified the first one (i.e. not the "other" child) as a boy

thus the only combinations possible are

1 2
B G
B B

if the phrasing were "What is the probability that both children are boys?" the answer would be 1/3.

The difference between the two phrasings is that in the first, the gender of one specific child is confirmed, and cannot change. However, in the second, both could change.

>>982939
There are three possible combinations: both boys, both girls, or a mix.

Ther are four possible permutations: BB, BG, GB, GG.

When we eliminate one possibility (GG) we have to recalculate the probability of the rest. What you SHOULD do is ue the number of remaining permutations (3) to get the probability (33.3%).

What most people are doing is incorrectly using the remaining number of combinations (2) and assuming they have equal weighting to get an answer of 50%.

You gaiz remember biology?

Male: XY - generates X or Y sperm
Female: XX - generates X or X eggs.

So... There's 3 X and 1 Y.
So there's 3/4 chances of being a girl!!!
You all suck!

>>982957
But
{one is a boy}
intersection
{the other is a boy}
=
{both boys}

>>982987

This is correct.

See http://en.wikipedia.org/wiki/Boy_or_Girl_paradox#Ambiguous_problem_statements

># From all families with two children, one child is selected at random, and the gender of that child is specified. This would yield an answer of 1/2, and many experts agree.[3][4]

>>983015
>implyng the trolls are experts or would agree.

if someone still doesnt believe it look up "conditional probability".

>>983015
But that's different.
In that experiment, a specific child is known to be, say, a boy.
In OP's hypothesis, either child could be a boy.

>>983047
In OP there's the known child: a boy.

And the other child.

Is it a boy? Is it a girl?

>>983047
Oh, I see what you did there.

>>983024
> if someone still doesnt believe it look up "conditional probability".
As worded, it isn't conditional. The second child is either a boy or girl. It has no bearing on the sex of the first.

>>983061
But you don't know which is the boy.

>>983024
So THAT's what CP means...

I've been searching it for years cause /b/ keeps asking, now I can give 'em! Yay!

I'm going back to saying 50%

>>983081
I do!
The known child is a boy.
The unknown child is either a boy or a girl.

Why would the time of birth matter and not the known/unknown child matter?

Its 25%. Draw a prob. tree faggot.

>>983081
you do.
read op question
one is a boy, the ___other___? asked is just the gender % chance of the ___other___ child, the one that is not stated to be 100% boy, so there are 2 possibilities, 50% girl or 50% boy.

disregard the boy child - its not important for the question.

>>983106
The time of birth has nothing to do with it. The fact that there are two distinct children does. And you know the gender of neither.

Saying that you know the gender of the boy is circular reasoning.

>>983127
It's in OP. I know he is a boy.
How's that circular reasoning?

>>983077
there is no "second" child since you dont know which is which.
<span class="math">P("What is the probability that the other child is a boy?" | "I have two children and at least one of them is a boy.")[/spoiler]

>>983125
Sorry, but I don't see how "the other child being also a boy" and "both children being boys" differ.

>>983141
But you know that the OTHER is not the one alredy spoken about, the one who is a boy.

ENGLISH, motherfucker, do you speak it?

It's 50%

>>983141
Fine. Not second; the other.

for fuck sake, this is not /b/, so stop saying its 50%

>>983127
I'll try this again...

>one of them is a boy
One is a boy.

>the other child is a boy?
OTHER, not the one alredy reffered.

So I know the one who is a boy is a boy and there's ANOTHER child who is the one OP's asking. There's no doubt he's asking about the gender of the other children.

Please, lrn2english.

>>983139
Because, in actuality, you know the gender of neither of the children. All you know is that there is a boy.

You're basically sayng that there is a boy, so we know the gender of one of the children, but that's not true, since either child could be the boy.

>>983191
Either children is the boy,
But OP clearly asks about the OTHER children.

>>983178
for op question the 100% boy does not count, asked is the _other_ child, which is 50% boy or 50% girl.

>>983187
But when you are speaking about "the other child", you could be speaking about either of the children.

here's a decent answer
http://www.codinghorror.com/blog/2008/12/finishing-the-game.html

There's A and B.
One is a boy.
It could be A is a boy and B is either boy or girl (50%)
It could be B is a boy and A is either boy or girl (50%)

>What is the probability that the other child is a boy?
>other
He's asking about the one not alredy assumed to be a boy.
So it's 50%.

Stop trying to troll, it's not working. But I'll keep feeding.

>>983208
You can't!
OTHER can't refer to this one, if you alredy said that this one is a boy.

i can't believe you guys are still talking about this shit.

OP's a faggot and fucked his wording up. >>982957

fucking /thread

>>983218
>>983218

>>983218
You're assuming that one of the two sentences is satisfied. That is correct. But we don't know which, so we have to take more probabilities into account.

>>983256
We don't know which, but it doesn't matter, because OP fucking said it didn't matter, 'cause he asked about the other child.

>>983224
But you haven't said that "this" one is a boy.
Maybe OP got his words wrong, but when I read
>at least one of them is a boy
I understand that either of them is the boy, so either of them could be the "other" one.

>>983269
this

answer to op question: 50% chance

>>983274
Either of them can be a boy, but the _other_ clearly means it is not asked about this one.

>>983269
>>983278
Again, you are talking about the "other" child like we know which is it. I can't really explain it any further. It's the same reason rolling 11 with two dice is twice as much likely than rolling 12.

>>983318
A or B is a boy.
If A is a boy, the OTHER is B.
If B is a boy, the OTHER is A.
It doesn't matter if we know who is the boy or who is the other, the other can not be this one.

>>>/b/229815536

man..
let <span class="math">\Omega = \lbrace b, g \rbrace ^2[/spoiler].
then let <span class="math">A = [/spoiler] "i have two children at least one is a boy"
obviously:
<span class="math">A = \lbrace bb, bg, gb \rbrace[/spoiler]
[mah]P(A) =laplace= \frac{|A|}{|\Omega|} = \frac{3}{4}
Now:
<span class="math">P("the other is a boy" | A) = \frac{P(A \cap "the other is a boy" )}{P(A)} [/spoiler]
<span class="math">=\frac{\frac{1}{4}}{\frac{3}{4}}[/spoiler]
<span class="math">=\frac{1}{3} \not \frac{1}{2}[/spoiler] ..

>>983318
We don't need to know who is the _other_.
But OP does and he asked about him.

>>983338
>>983218

Those two possibilities intersect on one area, which you forgot to deduct from your result.

Protip: its conditional probability

>>983363
>implying you don't know who the _other_ is.
The _other_ is NOT this one.

>>983405
Which one?

>>983421
>"I have two children and at least one of them is a boy"
This "ONE of them" this is the one who is not the other

>>983431
But we don't know which is the "one of them".

>>983437
But we know that the other is not this one. That's the meaning of OTHER.

You guys are all being trolled.

http://en.wikipedia.org/wiki/Boy_or_Girl_paradox

>>983456
If OP had worded it right, it would be that paradox, but he didn't.

>>983437
we dont need to know. one is a boy, the other is boy or girl.
stated is that one child is a boy, question is what the other child is.

>>983456
its not the paradoxon, read it, understand it.

>>983471
The article explains many forms of the paradox, one of which is OPs.
>>983440
So you're saying
>the other is not the kid which we know is male
>the male kid is not the one whose gender we want to find

right?

>>983502
>the other is not the kid which we know is male
>the male kid is not the one whose gender we want to find

Yes, exactly.

two boys chance is 1/4.. 50% for first and 50% for the second.. as u have a guaranteed boy its 50%.. your teacher can suck my dick if he/she insists that its 50%..

>>983516
Well, isn't the circularity between those two obvious? It's the same sentence inverted.

>>983537
It doesn't matter ,that's what OP asked.

Check it out:

There's two kids.
OP said one of them is male:
>One is male and we don't know who he is.
OP asked about the _other_ one, therefore, not this one above. So this one:
>One is either male or female and we also don't know wo he is.

>>983552
In either case, it boils down to, if
(a)A is a boy, so 50% B is a boy
(b)B is a boy, so 50% A is a boy,

we are looking for the probability of ((a) OR (b)).

Correct up to here?

>>983537
It's not just inverted.
It's clearly saying that who we want to know is not the one who we know it's male.

>>983580
It boils down to:
There's a kid A or B who is a boy.
There's _other_ kid, B or A who is 50:50, who OP is asking about.

>>983608
So:
If OP asked for A, it's 50%.
If OP asked for B, it's 50%.

Correct up to here?

>>983625
I guess...

I love how so many people are doing permutations instead of combinations.
In this case, BG = GB because order does NOT matter. If you don't understand why just look up combinations in mathematics and you'll eventually find something.

>>983608
no, op asks about the one who is not the stated boy.

tried the question in other languages, its always the same. other child =|= stated boy

ITT: faggots who don't know shit about statistics.

52% of humans are female.

This means that AT BEST, there is a 48% that the other child is male.

>>983639
l2math
there is no "in this case" since it all depends on how you define your model

>>983637
You could say that there is a 50% OP is asking for A, and a 50% OP is asking for B.

So, the total is 50%*50% + 50%*50% = 25% + 25% = 50%.

Correct up to here?

>>983675
I guess...

>>983659

Truth.

>>983681
Let me now state:
If Mr Smith has two boys, then OP could be asking 50% for A's, or 50% for B's gender.

Correct up to here?

>>983675
by that logic you have to account for two boys twice, since you dont know which one is the one the original speaker in the problem refers to.. which then again leads to the correct answer of 1/3. done.

>>983706
I guess...

Which either OP asked about A, who is a boy, or about B, who is also a boy, since you stated if they are both boys. right?

100%
1 definatley a boy is the other 0_o

>>983732
Right.

So, if both Mr. Smith's children are boys, both of the "if"s we stated at >>983625 are satisfied.

Right?

>>983754
Yeah, gottago, keep this thread alive until later tonight, okay?
sorry... Or keep it by mail srbrunoaf@hotmail.com I'm really not trollin.

Mr Smith says: "I have two children and at least one of them is a boy." What is the probability that the other child is a boy?

i have two children and at least one of them is a boy.
----------- ok, he has min 1 boy.
what is the probability that the other child is a boy?
------------ he asks for the child that is not stated to be a boy. the other.

wording in this one is important, the "other" is the gamebreaker, it reduces 2 children to 1 child. boy or girl. 50/50.

>>983768
OK.

But, to my train of thought, when I added the probabilities of the ifs at >>983675, I think I added the possibility "both boys" twice then.

Right, people?

>>983363

French???

>>983769

You are assuming "the other" refers only to the child that is not guaranteed to be the boy. If "the other" refers to the child who is a boy, then the answer is 100%.

>>983799
Can't stay on, see you on e-mail.

>>983832
i have no reason to assume that it does not refer to the boy. the wording is clear. op disregards the stated boy and asks for the other child.

>>983874

But you also have no reason TO assume. Inb4 god argument. Lack of evidence against is not evidence for (and vice versa).

>>983888
what i read: 2 children, 1 boy, disregard boy, what gender is other? = 50%
what you read: 2 children, 1 boy, pick blindly one of the 2, boy or girl? = 66%

both is possible the way op has worded it.

ITT: niggers