Math Tricks - make your life simple

[Classicclean]

Hey everyone,
today we had a small conversation about math and math tricks after Thaadevil asked for help in the bawx. I came with some 'tricks' and joked about a math tricks topic but many people said that they would like to see it. So what I'm going to do here is simply a collection of the math tricks I'm using in my daily life to make it easier. I wish I'd knew them when I was in the school =(

Multiplication:

11-19x11-19

For this example we take 18x19

This is really simple. At first, we gonna calculate 10x10 = 100. After that, we take the rest (8 and 9) and add them. 17 rest means 17x10 = 170 cause of every rest in the 10-19x10x19 'row' is worth 10. At the end we just multiplicate 8x9 = 72. Now we just add the three numbers
100+170+72 = 342

You can also do it with 21-29x21-29. This time every rest is worth 20.

25x26

20x20 = 400
(5+6)*20 = 220
5*6 = 30

650

31x39

30x30 = 900
(1+9)*30 = 300
1*9 = 9
1209

I guess you get the point

The higher the "rows" get, the harder this trick will become because you have to keep "higher" numbers in your mind. So my favourite trick for 91-99x91-99 is this one

95*96

-> 100-95 = 5
-> 100-96 = 4
-> 5+4 = 9
-> 100-9 = 91 <- first number
-> 5*4 = 20 <- second number
= 9120

97*98

-> 100-97 = 3
-> 100-96 = 4
-> 3+4 = 7
-> 100-7 = 93 <- first number
-> 3*4 = 12 <- second number
= 9312

get the point ?

square something

I've only got 2 tricks here. One trick for 41²,42²,43²,44²,45²,46²,47²,48²,49² and one trick for every 2 digit number with 5 at the end. For example: 35,55,85,95

Let's start with the first trick

43²

43-25 = 18 <- first number
50-43 = 7
7² = 49 <- second number

1849

46²

46-25 = 21
50-46 = 4
4² = 16

2116

Just take the number, subtract 25, write down. Then subtract your number from 50, quarter it, write it down. Your done

Now the trick with all 2 digit numbers ending with 5

45²

Take just the first number, multiplicate it with itself+1 and then add 25

45²
-> 4*5 = 20
-> put 25 behind it

2025

85²
-> 8*9 = 72
-> put 25 behind

7225

Any number * any number, only with drawing and adding. No multiplication needed



This looks really complicated. But it's not. You probably have to do it yourself and test it out with different numbers before you fully understand it, but as soon as you do, you are able to do it with just 1 color and therefore just 1 pen (I suggest learning it with 1 color anyway) and on a small piece of paper.

You simply write down the calculation. In my case it's 123x321

Then you draw vertical lines for number 1 and horizontal lines for number 2.

Now you have to mark the "areas".

Always mark the upper left area. Then go 1 field down, mark it, go 1 up 1 right and mark it.
Then you go back to the very left, take the last unmarked field, go 1 up 1 right, 1 up 1 right.
Now take the the nearest to the left, empty field that is possible. In this case it's in line 2 (the very down one), mark it, go 1 up 1 right.
Then take the last field.

It sounds very strange, but it's not that hard. Take the very left empty field (from up to down), if possible go 1 up 1 right. If not, take the next most left and empty field thats higher than another field. I hope you get the point

Now we just count the crossings And start on the upper left side.

Field 1 is 3.
Field 2 (count both fields together) -> 8
Field 3 (cound all three) -> 14
Field 4 (both) -> 8
Field 5 -> 3

Now simple add them together like this

3
08
 14
  08
   03
_____
39483

This is our outcome. Spend 30 minutes and you will get it, totally Just grab a pen and try

That's all for now. Have fun with that !

[CreativeXtent]

thank you lots for this <3

[HighFred]

Thanks for sharing as requested
Will +rep when I can, I need to spread

[KenMokai]

Thank You!

[Classicclean]

No problem mates, hope it helps !

[peterfried]

nice, thanks!

[Thaadevil]

You sir are a Mathoholic <3

[Classicclean]

Haha, thanks for the feedback guys!