Useful. pretty sure I'll forget it in like 5 seconds though. Mill I illegit THIS?! I Blir FE: Elf . WE! this Gilt , This is all if tn I " math easy useful Good to know
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Comments(147):

[ 147 comments ]
What do you think? Give us your opinion. Anonymous comments allowed.
User avatar #102 to #61 - mrselfdestruct (04/27/2014) [-]
on you go to top comment
#26 - derangedberger (04/27/2014) [-]
This trick just BLEW my mind!
User avatar #8 - brrigg (04/26/2014) [-]
i'm just gonna use a god damn calculator.

yall *********** be over complicating everything.
#16 - faktura (04/27/2014) [-]
**faktura rolls 97**
User avatar #23 to #16 - halloweenwillcome (04/27/2014) [-]
**halloweenwillcome rolls 41** Fak Tu ra
User avatar #34 to #16 - deadmansdope ONLINE (04/27/2014) [-]
**deadmansdope rolls 51**
User avatar #69 to #16 - ohhh (04/27/2014) [-]
**ohhh rolls 78** penis.
User avatar #119 to #16 - fishandkids (04/27/2014) [-]
**fishandkids rolls 70**
#65 to #16 - anon (04/27/2014) [-]
**anonymous rolls 42** allah ackbar
User avatar #32 to #16 - zerpderp (04/27/2014) [-]
**zerpderp rolls 12** we roll together we fail together
#19 to #16 - lastweek (04/27/2014) [-]
Now roll the rest of it!
Now roll the rest of it!
#4 - xehanortscrack (04/26/2014) [-]
This **** is stupid. Even if my example is incorrect and I got it wrong, it's still stupid because in most cases you'll end up having to divide and multiply large numbers anyways. Such as 15 x 68.
Just do as you were thought in school, it's much easier
Assuming you all were thought the same method as I was
User avatar #5 to #4 - xehanortscrack (04/26/2014) [-]
I just noticed that if I had added 17 to the 10 in 1020, then I would actually have gotten the answer which was 2720. However, this is not how it was show in the example above. Also, multiplying 85 and 32 is just as time consuming as multiplying 15 and 68.
User avatar #37 to #5 - alltimetens (04/27/2014) [-]
Adding 17 as an extra step is still way better than doing it conventionally.
User avatar #6 to #4 - whichever ONLINE (04/26/2014) [-]
100-83=17
put 1700
15x68=1020
add the two
2720
User avatar #7 to #6 - xehanortscrack (04/26/2014) [-]
Yeah, I noticed that, but that doesn't match the example above.
#73 to #4 - bknob (04/27/2014) [-]
>Just do as you were thought in school, it's much easier

will do
User avatar #1 - shadowm (04/26/2014) [-]
Just so you know it works for numbers not as close to 100 too, though it tends to be a little more difficult. 82 x 73 = 5986...100-82 = 18, 100 - 73 = 27, 18 x 27= 486, 18+27=45. Now here's the silly part, if the number of the mulitplication is triple digits you have to subtract the first number, in this case 4, from the addition, which is 45 so 45-4=41. 100-41=59, not add on the last two digits of your multiplication and you get 5785. 65 x 89 = 5785. 100-65= 35, 100-89=11, 35 x 11=385, 35+11=46, 46-3=43, 100-43=57, add on the 85 from the multiplication and you get 5785. Did it twice just to prove (mostly to myself) that it wasn't a fluke.
#64 - qballextraction (04/27/2014) [-]
86 x 93...ok I got this.  14 + 7 = 21 - 100 = 79.  So far so good, now to just multiply 14 by 7...			****		.
86 x 93...ok I got this. 14 + 7 = 21 - 100 = 79. So far so good, now to just multiply 14 by 7... **** .
User avatar #82 to #64 - hilariousrubbish (04/27/2014) [-]
arriety YEAAAAAAH BOOIIII
User avatar #121 to #64 - wiredguy (04/27/2014) [-]
you can't do 14*7 in your head?

(7*10) + (7*4) = 70 + 28
7*7*2 = 7^2 * 2 = 49*2

you just turn it into a mix of easier questions
#126 to #64 - lastsamurai (04/27/2014) [-]
14*7 = 10*7 + 4*7 = 70 + 28 = 98

I think of it like that.
User avatar #70 to #64 - brokentrucker ONLINE (04/27/2014) [-]
7x10=70
7x4=28
28+70=98

Do you even math? double times single digits are easy.
User avatar #72 to #70 - DmOnZ (04/27/2014) [-]
Or you could go up one and use 15 x 7

You know that 5 x 7 = 35

then it's just a matter of
35 + 70 = 105

and finish it off with
105 - 7 = 98
#79 to #72 - mrbjaecon (04/27/2014) [-]
or do 7x7x2 no double digits
#21 - hugsta ONLINE (04/27/2014) [-]
Tried it with 50x50 (simplest one that came to my head)   
Got some recursive 			****		, wrinkled my brain man.
Tried it with 50x50 (simplest one that came to my head)
Got some recursive **** , wrinkled my brain man.
#22 to #21 - notmadguy (04/27/2014) [-]
50 x 50 = 1002500

50 + 50

-----------
X

LOL




#110 - rothingham (04/27/2014) [-]
Cracked the math.



I have no idea why I did it though, I have much better things to do...
#131 to #110 - anon (04/27/2014) [-]
As a math teacher, I want to make a suggestion. When proving a formula to be equal to another, you can't cross one over the equals sign. You are trying to prove they are equal, and by moving values over the equals, you already assume they are. This could NOT work, but it might seem like it does because of how you solved this. I challenge you to try again though. I'm curious if you can actually do that. Show your work like you have here, and I'll give you some extra points on your next quiz.
#136 to #131 - rothingham (04/27/2014) [-]
As an engineering student, I don't care.
#140 to #136 - jonodillieono (04/27/2014) [-]
Well maybe you should care or you're going to fail since you can't do a proof correctly
User avatar #111 to #110 - givememoarpony (04/27/2014) [-]
i'd at least congratulate you for finding the obvious reason behind this instead of blindly parroting it like everyone else seems to be doing.
User avatar #113 to #111 - mytwocents (04/27/2014) [-]
the "formula" in OP's picture does NOT work for all cases just like that.
and because every mobile phone got a calculator - who cares...
#117 to #113 - anon (04/27/2014) [-]
Because it's helpful to understand why it works, for one, your mobile phone doesn't do **** if your serious about math. You wouldn't have your precious phone, computer, TV, medications, or any technology whatsoever if people didn't care to understand mathematics.
#120 to #117 - mytwocents (04/27/2014) [-]
> implying the OP's (not rothingham's) "formula" is about understanding algebra
#138 to #120 - anon (04/27/2014) [-]
That's not the point. You're saying who gives a **** about math? We wouldn't have **** if it weren't for math. Everything involves math.
0
#137 to #120 - ivviism has deleted their comment [-]
User avatar #114 to #113 - givememoarpony (04/27/2014) [-]
it's still the same simple idea of distribution of multiplication over addition.
User avatar #24 - demandsgayversion (04/27/2014) [-]
Until the day comes that we all carry calculators everywhere we go, we need to know **** like this.
User avatar #28 to #24 - jlew (04/27/2014) [-]
If you have a cellphone then you do carry a calculator everywhere you go.
User avatar #29 to #28 - demandsgayversion (04/27/2014) [-]
I know.
User avatar #30 to #29 - jlew (04/27/2014) [-]
Then that is all that is needed.
User avatar #31 to #30 - demandsgayversion (04/27/2014) [-]
I agree.
User avatar #60 - chism (04/27/2014) [-]
ya cause this will make 76X43 sooo much easier
#54 - kaarvaag (04/27/2014) [-]
This trick only work for 9X * 9X though.
Like, it doesn't work if it's 4X * 8X
#56 to #54 - juter (04/27/2014) [-]
That's why we invented Lattice. 			****		 mathematics without boxes.
That's why we invented Lattice. **** mathematics without boxes.
#36 - anon (04/27/2014) [-]
This only works for 91 - 99.
User avatar #38 to #36 - mummyslittlebitch (04/27/2014) [-]
What this guy said
User avatar #135 - thewalruss (04/27/2014) [-]
Use this methode to do this:
45 X 55
#141 to #135 - anon (04/27/2014) [-]
**anonymous rolled image**
#124 - konradkurze (04/27/2014) [-]
Comment Picture
User avatar #91 - herpedobear (04/27/2014) [-]
it's wrong.

according to this **** 86 x 90 should be 24140 but it is 7740
User avatar #100 to #91 - CPforPB (04/27/2014) [-]
having the same problem
#115 to #100 - anon (04/27/2014) [-]
me too, this is ******** :/
User avatar #128 to #91 - thunderdownunder (04/27/2014) [-]
100-86=14, 100-90=10

14+10=24, 100-24=76

14x10=140

So this method makes it look like it's 76,140 but the trick is when it gives you a number above 4 digits is to add the first digit of the 140 we got from multiplying the 14 and 10 to the last digit of the 76 we got from subtracting the answer of 14+10 from 100 and you get 7740
#78 - psykobear (04/27/2014) [-]
Except that there is a much easier method that actually works all of the time, for numbers of any size.
I present: The Lattice Method
9x9=81, 7x9=63, 9x6=54, 7x6=42
2=2, 4+4+3=11(or 1, carry 1), 1+1+6+5=13(or 3, carry 1), 1+8=9
9312
#80 to #78 - psykobear (04/27/2014) [-]
Another, just to show it works with larger numbers
User avatar #83 to #80 - darthblam (04/27/2014) [-]
This was the only method I was able to use to multiply..

To this day I still have no ******* clue how to do it in the more common way.
User avatar #88 to #78 - Zydratejunkie (04/27/2014) [-]
Teach me.
What numbers are we multiplying, and how to you get all the other numbers.
#108 to #88 - anon (04/27/2014) [-]
Never even seen this method before, but here goes.

Each big box is split into two - Tens/Ones, from multiplying the two side digits. EG, you get 6/3 from multiplying 9 and 7 (9*7=63), and 4/2 from 6*7
Then you start from the bottom right, which each diagonal row being a separate units column. In this case, 2 is the first digit. Then 3+4+4 = 11, so 1 is the second digit and the 10 carries across into the next. So then you have 1 + 6 + 1 + 5, which equals 13. Again, the 10 carries across and 3 is your 3rd digit. Finally, 1 + 8 = 9, giving 9312

Seems a bit confusing to me, but if you've grown up with it it makes a lot more sense.
User avatar #143 to #108 - psykobear (04/27/2014) [-]
Anon is exactly correct.
#134 to #78 - rokulda (04/27/2014) [-]
WHAT THE 			****		 IS THAT
WHAT THE **** IS THAT
User avatar #144 to #134 - psykobear (04/27/2014) [-]
An easy way to multiply, once you understand how it works.
User avatar #94 to #78 - capslockrage (04/27/2014) [-]
I don't even know what the **** i'm looking at and really don't feel like figuring it out.
User avatar #66 - iridium ONLINE (04/27/2014) [-]
Or you can just figure out the mental shortcuts. Or better yet, write it down or use a calculator? Most phones have calculators these days anyways.
#71 to #66 - anon (04/27/2014) [-]
calculators are for retards. unless you doing trig/calc and **** like that.
User avatar #84 to #71 - darthblam (04/27/2014) [-]
******* **** trigonometry, ******* christ, trigonometry is why bad things happen in the world. Trigonometry would make a Buddhist monk strangle a ******* puppy, I swear to god I hate trigonometry.
User avatar #89 to #84 - samous (04/27/2014) [-]
Trigonometry is why I hate math
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