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/sci/ - Science & Math

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5693506 No.5693506 [Reply] [Original]

itt: We discuss tricks and useful methods to do Mental calculation.

> Asians are more than welcome for this particular thread.

>> No.5693510

how can you tell which ones are Asians?

>> No.5693511

>>5693506
the picture does an unnecessary extra step. you could just subtract 4 from 97 or 3 from 96, that's how I do it

>> No.5693514

75*88
100-25 = 25
100-88 = 12
25+12 = 27
100-27 = 73
12*25= 300

75*88 = 73300

durr hurrrr

>> No.5693515

>>5693511

but are these ways of thinking, when trying to avoid a calculator actually worth it, or does it just make everything even more confusing?

>> No.5693517

>>5693515
I use these tricks all the time

>> No.5693519

>>5693514

(100-25) *(100-12) =10,000 -3700 +300

I wasted both our time. You're welcome.

>> No.5693520
File: 9 KB, 264x191, imgres.jpg [View same] [iqdb] [saucenao] [google]
5693520

>>5693514

>100-25 = 25
>25+12 = 27
>75*88 = 73300

well done.

>> No.5693521

>>5693517

Cool, got any tricks you feel like sharing? :)

>> No.5693525

>>5693521
a magician never shares his secrets

>> No.5693535

>>5693514
75*88 = (100-25)(100-12) = 10000 - 2500 -1200 + 12*25 = 10000 - 3700 + 12*100/4 = 6300 + 12/4 * 100 = 6600

>> No.5693553
File: 48 KB, 470x432, datkitten=p.jpg [View same] [iqdb] [saucenao] [google]
5693553

>>5693506
I did something similar to this converting km to miles.

I was like 11 or something. My parents just told me "that's not how you work it out".

It works every time and I still use it.

>> No.5693563

>>5693535
>>5693519
yes, obviously, but the procedure outlined in the OP clearly doesn't work for most two digit numbers.

>> No.5693565

I just use foil on a product of sums

>> No.5693568

moar tricks pls

>> No.5693569

>>5693563
using de facto statements
>obviously
being wrong
total pleb

reclaim your honour, consinder harakiri

>> No.5693574

>>5693569
alright let's try it again.
37*87
100-37=63
100-87=13
63+13=76
63*13=819
87*37=76819, according to that piece of shit image posted in the OP

hurr durrr durureffef

>> No.5693578

>>5693514

75*88
100-75 = 25
100-88 = 12
25 + 12 = 37
100-37 = 63 (*100) = 6300

25*12 = 300

6300+300 = 6600

>what are you fucking doing?

>> No.5693579

>>5693574
wtf are you doing?
2400+819 = 3219

seppuku right now, I demand it!

>> No.5693581

To square a two-digit number that ends in 5;
>The answer begins by multiplying the first digit by the next higher digit.
>The answer ends in 25.

example

35^2 is 1225 because the first digit 3 is multiplied by it's next integer sequence '4' giving 12 in the beginning. the answer will end in 25, therefore it is 1225.

55^2 is also 3025 because (5*6) gives 30, the answer will end in 25, giving the result 3025

>> No.5693582

>>5693578
>100-37 = 63 (*100) = 6300
Where did the OP image say that?

>> No.5693583

>>5693581
so cool

>> No.5693584

>>5693579
you're right , you're right. I'm sorry I did make a mistake.

37*87
100-37=63
100-87=13
63+13=76
100-76=24
63*13=819
87*37=24819, according to that piece of shit image posted in the OP

>> No.5693586

>>5693582
>not knowing place values
what are you, ten?

>> No.5693590

>>5693584
the 4 and the 8 are in the same place value, is you gut bloody yet? for the sake of your ancestors

>> No.5693591

>>5693525
this

>> No.5693597

>>5693510
The one in OP is a Indian method.

Anything developed by asians = asian method

>> No.5693598

>>5693590
says who? The image in the OP?

Because the image in the OP says that whatever the orange number is comes first and whatever the blue number is gets placed after the orange number, then that gives you the answer.

>> No.5693599

>>5693591
thouse are lame magician words, we are here speaking about math, everybody should know all the tricks, and try to find new ones!

>> No.5693602

>>5693599

this

>> No.5693603

>>5693598
use some common sense

>> No.5693609

>>5693602
this what?

>> No.5693608

>>5693603
>apologism for an image showing an incorrect procedure

Great mathematics bro

>> No.5693613

>>5693598
>>5693608
if you want to follow instructions without thinking, let me help you poor head.
do you notice the 12 is 1 in the ten's place 2 in the one's
so if you have a value that is 819, the 8 is in the hundred's place.
your lack of maths skill displeases me, bro

>> No.5693618

>>5693613
could you explain it more clearly?

>> No.5693625

>>5693618
I think you seriously need learn about place values. try khan academy, go there quick before your ancestors come out from the ground and tear you limb from limb for your disgrace

>> No.5693626

Slight easy

But if you ever want to multiply a number by 5, stick a zero at the end and halve the number or vice versa

<span class="math"> 5n = \frac{10n}{2}[/spoiler]

>> No.5693635

>>5693618
here found it for you
http://www.youtube.com/watch?feature=player_detailpage&v=iK0y39rjBgQ#t=128s
just watch it from this point

shit a 7 year old learns

>> No.5693644

>2013
>still not knowing place value system

>> No.5693645
File: 13 KB, 195x300, 001248de_medium.jpg [View same] [iqdb] [saucenao] [google]
5693645

>>5693525
>a magician never shares his secrets

pic related, you can get this at piratebay. No such thing as secrets in math.

>> No.5693649

>>5693645
oh yes there are, shhh!
.
.
.
psst, tell me the algorithm that matlab uses!?

>> No.5693652

Why /sci/ threads never reach more than few comments, is it a secrete rule you have? This seemed interestng, but nothing, a few stupid coments and its over.

>> No.5693658

>>5693645
>No secrets in math
>Title "secrets of mental math"
>mfw

>> No.5693661

>>5693652

/sci only likes to argue about religion and pretend they know how to apply logic during arguments

this thread doesn't allow for either

>> No.5693670

>>5693658
jajaja

>> No.5693674

>>5693661
and why? this could be a great place to speak and learn about physics and math

>> No.5693677

>>5693674
>could

too bad it isn't

>> No.5693680

>>5693645
http://libgen.info/view.php?id=906312

>> No.5693698

Not really that useful, but I'll share it anyway.

To cube root numbers that are two digit numbers cubed e.g 46^3 = 97336

(prerequisite: learn cubes of 1-9)

1) Split the number so the hundreds are on the right: 97 | 336
2)look at the left side and choose the cube number that is closest to it, but not greater than it. So in this case 4^3 = 64, 5^3= 125. You choose 4^3 as it's less than, but closest to 97.

This number cube rooted will be the tens digit.

3)Look at the number on the far right (6). Each number cubed from 1-9 results in a separate number for the first digit. They are all the same as the number itself except for 3 is swapped with 7 and 2 is swapped with 8.

2^3 = 8 , 8^3 = 512 etc.

In the example 336 ends with 6 and therefore it corresponds with 6^3. This number cube rooted is the unit digit.

4) Put them together : 46 Tada!

More of a party trick really, but I've used it several times when working out problems.

>> No.5693728

>>5693698
Also here's a way I like to use to multiply two two digit numbers in my head. (requires you to recall multiplying up to 10*10 instantly due to carrying things around in your head).

e.g. 64*96

write them like this:

6 4

9 6

1)multiply the diagonals and add them. (6*6=36 + 9*4=36 = 72)
2)shift the number to the left by one digit (multiply by 10) and add the product of the units (720 + 24) = 744
3)multiply the tens column together and multiply by 100 then add to the rest. (6*9*100 =5400)

5400 + 744 = 6144.

It's important that you add some tricks to help you remember the numbers that you're storing as you only can hold 7 +/- 2 bits of information in your head at a time.

If you're able to visualize things well then try picturing the numbers in your head when your doing the sums. If you're left brained it probably means that you're good with remembering things when they're heard so try saying the numbers in your head.

>> No.5693731

>>5693728
http://youtu.be/9gQ7s58gZdU?t=13m15s

here's a video about the things you can do with vedic maths. Apparently even being able to solve integrals which require doing them by parts instantly.

>> No.5693735

A challenger appears
https://www.youtube.com/watch?v=M4vqr3_ROIk

>> No.5693758
File: 50 KB, 580x435, 1363062240429.jpg [View same] [iqdb] [saucenao] [google]
5693758

>>5693506
>inferior version of that pic

>> No.5693768

This is probably well known but finding out if something is divisible by 3 is super easy.
Add all the digits together and if that number is divisible by 3 then the original number is. The process can be repeated for large numbers.
e.g.
42: 4+2=6, yes
699: 6+9+9=24, 2+4=6, yes
123489: 1+2+3+4+8+9=27, 2+7=9, yes

Can also be used to disprove that something is divisible by6,9,12 etc.

>> No.5693776

>>5693731
looks like a bit of a scam
>here is what you can do
>go to my website
>by my book

>> No.5693781

>>5693776
Yeah this particular website seems to be a scam, but vedic maths is a system so you can probably learn it from somewhere else.

>> No.5693782

>>5693768
see also:
a number is divisible by eleven if you alternate adding and subtracting from the largest power of 10 to the 1s and it adds to zero
e.g.
121-- 1-2+1=0
11-- 1-1=0
just gonna make this one up on the fly:
2-4+1-3+5-1=0
241351 can be divided by 11

>> No.5693807

>>5693735
Cool, I always wonder if people used a word code for their calculations, I've never found time to develope my own. I wonder why this is kept like a secret instead of tought...

>> No.5693809

>>5693807
I mean, I have my code, but not an efficient way to combine it with calculations, converting and unconverting is kind of a slow proccess, I think

>> No.5693854

>>5693680
Best mental math book ever. All you need to know is inside there

>> No.5693858

>>5693626
Arent you a genius

>> No.5693859

>>5693858
lel

>> No.5693860

http://www.youtube.com/watch?v=9gQ7s58gZdU&feature=youtu.be&t=13m15s

Has somebody find this dvd/books for free? looks powerfull

>> No.5693862

>>5693563
it does even work for 3 (and more) digit numbers, to multipy x and y:
red part:
<span class="math">(100-x)+(100-y) = 200-(x+y)[/spoiler]
<span class="math">100-..[/spoiler] to get result digits <span class="math">100-(200-(x+y))[/spoiler]
shift result by 2 digits left: <span class="math">100 \cdot (100-(200-(x+y)))[/spoiler]

blue part:
<span class="math">(100-x)(100-y) = 10000 -100(x+y) + xy[/spoiler]

together:
<span class="math">100 \cdot (100-(200-(x+y))) + (10000 -100(x+y) + xy) = [/spoiler]
<span class="math">10000 - 20000 + 100(x+y) + 10000 - 100(x+y) + xy =[/spoiler]
<span class="math">xy[/spoiler]

>> No.5693872

what about mental abacus? Does anybody know something about that?

>> No.5693874

>>5693872
That's how the Japanese learn math isn't it?

>> No.5693875

>>5693874
Chinese and Japanese. And maybe koreans.

>> No.5693882

>>5693874
I've seen videos, and it is pretty impresive but I have no idea how they do it mentally..

>> No.5693889

>>5693882
They do it a lot when they're younger so it becomes a reflex to them. When something becomes a reflex, they take away the abacus and kids still make the hand movements as though the abacus was still there.

The final stage I guess is where they don't need to use hand movements anymore.

Also here is a really good link I found to do with mental algebra.

http://boostmath.com/mental-algebra/introduction/

>> No.5693902

>>5693889
>>http://boostmath.com/mental-algebra/introduction/

Not bad

>> No.5693912

>>5693902
The trouble I'm having with it, is that it requires you to visualize the equation in your head. I cannot see anything unfortunatly.

>> No.5693918

>>5693872
Does this worth time wasting?
Or our system is ok

>> No.5693921

>>5693918
Not really worth it as being a human calculator isn't that useful and they do it when they're kids so they learn how to do it easier.

>> No.5693922

>>5693912
ehhhh? really?
You cant see things?
Then what? you just hear things?
you can not visualize equations?

I mean...at least you dream at night, or no?

>> No.5693924

>>5693921
It do not worth depending on the time that it takes to learn that... I wouldnt mind being able to avoid the calculator, dont you?

>> No.5693926

>>5693912
I'm really interested in this, how clear can people visualize things.

>> No.5693928

>>5693912

I do not beleave it, when you say that you cannot visualize.
Everyone can.
Though it is limited on how many things you can visualize at a time. But with the proper methods and ways of thinking you may be able to do so.
Hence the reason why i brought up this thread : )

>> No.5693934

>>5693928
>>Everyone can
I'm not sure if that's true...

>> No.5693940

>>5693934
I recently found that some people hear a voice when they read, an other peoplo do not. Quite impresive.
It would not be extrage if some people can not visualize things... I do not know

>> No.5693961

>>5693902
This is quite good, advance a few chapters. It is how I like (and I supouse everybody) to see to an equation.

>> No.5693975
File: 73 KB, 476x484, Descartes.jpg [View same] [iqdb] [saucenao] [google]
5693975

Extracting cubic roots from numbers up to 1000000 (the result must be integer or it won't work!)

1. You need to memorize this table:
03 = 0
13 = 1
23 = 8
33 = 27
43 = 64
53 = 125
63 = 216
73 = 343
83 = 512
93 = 729

2. Note that the X3 values for the 10 digits all have different ending digit, so inverse table is:
0 => 0
1 => 1
2 => 8
3 => 7
4 => 4
5 => 5
6 => 6
7 => 3
8 => 2
9 => 9
It's all in order, just 2 swapped with 8 and 3 with 7, so pretty easy to memorize.

3. Now, given a number XXXYYZ, from which you need to extract the cubic root (XXX for 6-digit numbers, XX for 5-digit, X for 4-digit). For example 195112 => XXX = 195 , Z = 2

First, find the largest number smaller or equal than XXX from the first table: 195 => 125 => 5
Second, find the digit matching the root for Z from the second table: 2 => 8
The cubic root of 195112 is 58

Another example: 2197
X = 2 => 1
Z = 7 => 3
133 = 2197

>> No.5693979

>>5693613
by this logic, the 93 has a 3 in the units column and a 9 in the tens column, so the answer should just be 93 + 12 = 105.

but no, what the image actually says is that you should subtract each of the 2-digit numbers you're dividing from 100, then first add these two new numbers together, and subtract that sum from 100 and that will give you the first digits, however many there may be, of the answer to the original question. Then in order to get the last digits, however many there may be, of the original question, you instead multiply the two new numbers that were obtained by subtracting each of the original numbers from 100.

the picture specified nothing about overlapping of unit columns or tens columns or hundreds columns or anything else. It simply showed one number forming hte first however-many digits and one number forming the last however-many digits.


That's why it is garbage.

>> No.5693980

>>5693975
4chan ate my "^3"

>> No.5693987

>>5693922
>>5693926
>>5693928
>>5693934
>>5693940

Honestly I can't. I've posted on here before about this. It's like when you think about an idea two processes happen:
- You process the idea and bits of information about it, so when imagining a field, the idea of grass, a couple of trees and flowers are processed
- The picture formulates in front of you based on memories

For me the second process doesn't happen.

What's even weirder is that I can perform spatial reasoning tasks exceptionally well, as if the process is working, I just don't see the picture.

Another weird thing is that I can create very complex symphonies in my head even though I have never had any musical training.

To me it seems as though you guys have some sort of superhuman power being able to see things when they're not actually there.

http://discovermagazine.com/2010/mar/23-the-brain-look-deep-into-minds-eye#.UV9dnZOL1Bk

I've done quite a lot of research about it.

>> No.5693990

How to do mental calculation

Step 1: Look at problem
Step 2: Remember the numbers.
Step 3: Pull out calculator and write the remembered numbers down
Step 4: Remember the result
Step 5: Place result on paper

Woo!

But in all seriousness I probably overly rely on my calculator (to the point I can't instantly confidently tell you what 4*7 is without adding four to 4*6)

>> No.5693995

>>5693990
Plus, counting the spots on the numbers to do simple addition and subtraction I probably should have memorized instead

>> No.5693996

>>5693987
And dreams?

>> No.5694001

>>5693987
How do you fap man when no internet?

>> No.5694012

>>5693996
Really tough to put into words but I don't see anything. The whole "do you dream in black and white or colour" thing never made sense to me. Apparentely when people dream they see things like a movie. When I found out about this my mind was blown.

It's almost as though my mind tricks me into thinking that I'm seeing things. I know everything that's going on, I know what color clothes people are wearing, but I just can't see anything. I guess you could say that I dream about ideas.

>>5694001
Again this is a weird one. I prefer to fap using my imagination rather than watching porn. I tend to place more emphasis on feeling and sound rather than seeing things. But it's not as though I'm fapping to a blank wall. It still feels as though I'm seeing things even though I'm not.

>> No.5694014

>>5693987
Maybe you are confused... I (and I think most of the people) do not really see something when we imagine... maybe you are being picky, I mean... I see it, but not to the point to confuse it with reality... Its not completely precise or detailed... For me its only precise when I dream, I do not know if somebody can imagine to the point to confuse it with reality (not incluying deseases)

>> No.5694018

>>5694012
My dreams are no different to reality... unless strange things happend. I use to have lucid dreams (waking up in a dream, and doing (fucking) what you want), and really, they are just the same as reality, really no difference (unless multiplayer)

>> No.5694020

>>5694014
That's what I used to think, but my mum can actually see things and many others can too. I ask her to imagine a square and she said a red cube appears with a blue background. Obviously this ability varies from person to person.

>> No.5694026

>>5694020
Humm... really extrange... The dream thing really bothers me. I mean... you are not blind, arent you??

You can see things... And you said you can remember sound...

hear a sound, repeat it in your head. Do de same with vision, look at a thing, close your eyes, and do the same! repeat the image!!

Its extrange... I thought seeing and imagine is mostly the same

>> No.5694025

>>5694018
See that still blows my mind. So can you perform math equations in your head? My thought is that if you can see it, then you can rearrange it?

>> No.5694029

>>5694025
The original image, what im seeing, does not change, what I imagine is like superpoused, and not as detalied enogh in order to read it (depends on how big is what you are imagine, is... ) its like recalling a long song, you may recall the melody but not all the chords with precission.

Same for an image, or an equation, I can see the shape, I see that there were 3 terms, one is squared for example because I see it has something over it, but I may not recall the exact numbers...

>> No.5694030

>>5693862
QED

>> No.5694036

>>5694026
Nothing appears. It sucks, it's almost as though I haven't trained that part of my brain and because I haven't used it, it's stagnated and I can't use it at all.

>>5694029
Ah I see. I guess it varies a lot then. Some people can probably picture the equation in detail.

I wonder if you can perhaps practice it to get better at it.

>> No.5694044
File: 113 KB, 1235x1035, m22222.jpg [View same] [iqdb] [saucenao] [google]
5694044

50*50=

100-50=50
100-50=50
50+50=100
50*50=

100-50=50
100-50=50
50+50=100
50*50=

100-50=50
100-50=50
50+50=100
50*50=

100-50=50
100-50=50
50+50=100
50*50=

100-50=50
100-50=50
50+50=100
50*50=

100-50=50
100-50=50
50+50=100
50*50=


......

>> No.5694046

>>5694036
you can get better, but It's "impossible" to imagine 100% detailed... then you would have perfect memory... you would just look to a picture with 100 numbers and you would recall it, and as far as i know nobody can do that.

>> No.5694053

>>5694036
I still do not believe you 100%, I think you are simply beeing picky...

When you close your eyes, doesnt it take a while (milisecnods) to disapear what you are seeing?

I mean, when you close your eyes... everything goes black instantaniouslly?
Try closing your eyes really fast. What happens?

>> No.5694058

>>5694053
Try looking at something that emits light (also know as lamp), when you colse your eyes a spot remains, visual images are exactly like that, is like what you are seeing stucks for a while, like the light. If you want to feel how it is like, do the experiment. Maybe if you understand how it is like you can train yourself some how and reach visual imagination

>> No.5694063

>>5694053
It goes dark with loads of tiny flashes. However if I'm looking at a light source and then I close my eyes it goes black but with the shape of the light source still being present. It fades pretty quickly.

>>5694058
I've tried that with a white triangle on a black background on my monitor but I haven't noticed any improvement. It just disappears after a few seconds and when I try and keep it there nothing happens.

>> No.5694075
File: 69 KB, 1890x1540, Calc.jpg [View same] [iqdb] [saucenao] [google]
5694075

>> No.5694082

>>5694063
Well, at least you know what its like more or less. The thing is that I do not know how , but I can mantain that image as long as I want, and move it etc...

but its not like i'm seeing it with my eyes, indeed if I pay attention in what I'm seeing the visual image fades and disapears.

Im mean you can not train it just looking at something and waiting... you have to do something with your head, I do not know what. But just staring at things wont help (I think)...

I think the best way may be with dreams... If you took control and experiment, you hay visualize something, and with that you may have something to practice until you can controle it and try it awake.

Or you may relax, its not vital to visualize things, although it is really usefull. I used to train my self to improuve the quality of my imagination (details).

Give Ludic dreams a try...

>> No.5694083

>>5694082
I ment lucid

>> No.5694116

>>5693597
but india is in asia...

>> No.5695308

>>5693506
our