/sci/ - Science & Math

regarding your pic, OP: what the fuck? is it just me or 20 minutes is the right answer?

nah, amount of pieces is proportional to time.
to saw it into 1 piece is 5 minutes.
sawing it into 2 pieces takes twice as long, so 10 minutes. sawing it into 3 pieces take 3 time as long as 1 piece.
so 3X5 = 15 minutes.

20 minutes would be to saw it into 4 pieces.

yeh, just an example of why the US education system is failing haha.

>>2976848
Yes

>>2976858
Troll or retard
It takes 10 minutes to cut once to have 2 pieces. It will take another 20 minutes to cut again to have 3.

>>2976864
why does the next cut take twice as long? thats 30 minutes in total. it says she works att he same speed.

@EK it only takes 1 cut to cut a board into 2 pieces and therefore only 2 cuts to cut it into 3 pieces

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>>2976858

>to saw it into 1 piece is 5 minutes.
>derp

>>2976858
>cutting something into 1 piece

>>2976858

You best be trolling.

If you cut a board in half. It takes a certain amount of time. 1 cut in half = one fixed amount of time.

Just because you cut something twice, doesnt make the rate at which you made each cut faster.

A = LW
(L-2s)(W+4s)
LW+2ls-2sw-8s2

Something something answer asnwer

OP HERE, that was no the question haha, does anyone know how to solve the question i posted?

>>2976858
what does "to saw into one piece" even mean?
way i see it: 1 cut takes 10 minute, so 2 cuts (which produce 3 fucking pieces) take 20 minutes.

ahahahh
trolololol.

>>2976815
Ill help OP. Think of the formula for the area of a triangle. Now think of the differential shit you learned so far. Try to model it.

>2976875

thanks a lot i'll try now

Guys I tried to cut a board into one piece once. I took me like, an hour. Im never doing that again.

>>2976815
WTF OP?
S=L*W
S'=L'*W+L*W'=-2*10+4*13=32cm^/s

>>2976815
That picture makes me hate with all the power of my soul.

Regarding your question, OP, I'm going to give you a few obvious and probably not helpful answers.

First, it's a related rates problem, and the question asks you for A'. A=LW, and you can implicitly differentiate and plug in numbers pretty easily if you rewrite in terms of only l's or w's. The trouble is that you've got to account for the L and the W as well, and I'm not entirely sure how that should be done. If I had to guess, I'd find the rate of change of A with only L decreasing and then only W increasing, find the rate of decrease at L=13, find the rate of increase at W=10, and combine them. No promises there though.

lol, cant believe how many responses that got. sorry for derailing the thread OP.

>>2976897

> implying that your post wasn't serious

>>2976897

change in A = (13-2t)x(10+4t)
-8t^2 + 32t + 130

<span class="math">\frac{d L}{dt} = 2[/spoiler]
<span class="math">\frac{dW}{dt} = 4[/spoiler]
<span class="math">Area = L W <span class="math">
\frac{d Area}{dt} =\frac{dL}{dt} W + \frac{dW}{dt}L
\frac{d Area}{dt} =2*10 + 4*13
\frac{dArea}{dt} = 72\frac{cm}{sec} [/spoiler][/spoiler]

>>2976900
>>2976897

EK is like the boy that cried wofl. Except that instead of saying wolf, she just says something retarded.

>>2976897

>2976889
thanks heaps hahaha, didn't realise how simple it was

pff, i'm insulted you guys actually think i'm stupid enough to believe its possible to cut it into 1 piece.
its already in 1 piece, if its still in 1 piece you havent even cut it.

>>2976906
whoops, misread question;
<span class="math">\frac{dt}{dL}=-2[/spoiler]
\frac{dt}{dW}=4
Area=L*W
<span class="math">\frac{d Area}{dt} =\frac{dL}{dt} W + \frac{dW}{dt}L [/spoiler]
<span class="math">\frac{d Area}{dt} =-2*10 + 4*13[/spoiler]
<span class="math"> \frac{dArea}{dt} = 32\frac{cm}{sec}[/spoiler]

>2976906
can you please explain your post. what does frac mean?

thanks OP

>>2976906

I hate to be picky. But ultimately, you've written:

Area = 72cm/sec

And that is confusing as fucking hell for amateur math students, when people use equal signs loosely like that.

OP, you are making me rage... to post reference just click on the persons number, don't greentext and type it in, because it isn't even a link, and you are writing it in slowhand when you can have it as an automatic input.

>>2976923
fffuck
you get what I mean, put the correct values in the correct place
the answer is 14

>>2976907
Nailed it.

>>2976922
>pff, i'm insulted you guys actually think i'm stupid enough to believe its possible to cut it into 1 piece.

You're not?

>2976929
my comp is fucked. can't click any active scripts on any website for some reason.

>>2976922

>>2976934

put two of these in front of the post number >>

>>2976934
er..okay.

well anyway, its a double >> and then the number you want to reference, not a single >

>>2976935
wat?
and i lol'd on the 3rd clip he misses the pot...

>>2976943
EDIT: he misses on the 4th pot.

>>2976943

>>2976952
you have some strange gifs...

Area = W x L

d(Area)/dt = L x dW/dt + W x dL/dt
d(Area)/dt = 13*4 + 10*2
= 72 <span class="math">\frac{cm^2}{sec}[/spoiler]

>>2976906
>>2976974
same mistake I did, <span class="math">\frac{d L}{dt} = -2[/spoiler]
I also naffed up on my tags

pic = or > your teacher

Both 15 minutes and 20 minutes can be correct.

Imagine we have a plank with a length and a width of 'x'. Sawing 'x' takes 10 minutes. So, whether we cut the length or the width, cutting the plank in two pieces takes 10 minutes. Now, we have two planks: both of them have a lengt of 'x' and a width of '0.5x'. Now, depending whether we cut in length or in width shall decide whether it will take 5 minutes, or 10. If we cut the length, in other words 'x', we will have to add another 10 minutes to our original 10 minutes, resulting in a total of 20 minutes. If we cut the width, in other words '0.5x', we will only have to add half of 10 minutes because the amount we have to saw is just half of the original, thus resulting in a total of 15 minutes.

The problem is that the question does not specify the dimensions of the plank nor does it say whether the pieces are supposed to be of equal size. Cutting off two corners will also result in the plank having been sawed in three pieces, for example.

tl;dr: shitty question

>>2977055
there was a whole thread about this before. notice that on OP's picture the 'plank' is a very thin rod of wood,
so it isnt a flat square board like you are imagining.

secondly, you can invent an infinite ways to make smaller cuts and make more pieces. on your square board analogy you could cut off a tiny segment from one of the corners, and you would have made an extra piece, in not much time at all.

presuming that all cuts are the same length, (so you cut the width of the board, and then the width of the board again) then the answer is 20 minutes.

>>2977055
sorry my bad, i only read the 1st half of your post and then guessed the rest of it to save me some time. you already mentioned the corner thing.

>>2977064

My point was that the question is shitty exactly because there are so many possible answers. If however the question is rephrased in such a way that all cuts have to be of the same length, then the answer is indeed 20 minutes.

The teacher in OP's pic is not retarded because he chose the wrong answer, which he didn't, but because he didn't recognize that pretty much any answer is correct.

>>2977078
no, the teacher is still retarded. look at how they justify the answer for 15. it was the same thing i put in my trollpost, it implies 5 minutes to make 0 cuts.

>>2977081

Glancing over OP's picture again indeed makes it clear what thinking process the teacher used to get to his answer, which indeed is pretty much retarded. Surely a teacher of all people should be able to think logically?

>>2977085
becoming a teacher is not particularly difficult.
intelligence not necessarily required, particularly to teach low level maths like that.

>>2977085
lol, also, use grammar.
"surely a teacher, of all people, should ..."

otherwise it means 'someone who teaches all people'

>>2977092

>>2977089

I fear for the future when a teacher, nay, when any person cannot solve such an easy problem.

>>2977095
punctuation, not grammar. my bad.

>>2977092

Bitch, I'm too gangster to use commas.

>>2977097
meh, its forgivable. if you glanced over the question and didnt think about it properly and just saw the numbers, you would see the change from 2 to 3 as an increase of 50% and apply that 50% to time for the answer.

you have to realise that cuts = n-1 (where n = number of pieces after the cut)
so realise you should be considering 1 cut to 2 cuts, an increase of 100%, and apply that to time.

>>2977110

> if you glanced over the question and didnt think about it properly

I'm not sure what's worse: a teacher not having the intelligence to find out the right answer, or a teacher not having the patience to read the question properly.

>>2976815

The question is unambiguous and the teacher is wrong.

Also EK, you SUCK. AGAIN.

Yeah. I'm THAT dude again

>>2977124
its understandable. marking, like any repetitive task, is something people get bored with, they try and take shortcuts, skip steps and get the work done in the lowest possible time.

similarly, i didn't fully read >>2977055 and so i repeated what he already said about the corners.

its like, whenever someone posts 'shit is so cash' again, you dont fully read it, you read the first line, realise what it is, and presume the rest of it is what you remember it to be, so you can post a reply to something you have only partly read.

>>2977131
i suck, you agree with me?

fine by me. if i can only have one, i prefer to be correct rather than admired.

Ah I see. There are 2 groups here: Those that are looking at this in a mathematical sense, and those that are looking at it in a physical sense

I hope that retarded tripfag is an English major...

>>2977143

Either way the answer is the same, so exactly what are you trying to say?

>>2977148
No, zoology major. But speaking and writing properly is worthwhile.

>>2977148
EK's underage. Someone please ban him.

>>2977176
I'm majoring in zoology, therefore ive clearly passed high school, therefore i am clearly overage.
you're talking shit.

neeever mind the more I look at it the more I realise my logic fails

1 cut = 10
2 cuts = 20

if it was 'creating' pieces the teacher would be correct

2 pieces = 10
3 pieces = 15

:S

DONT HATE!!!