Mathematical Solutions: Multiplying by 9

We've always wanted a faster way to solve math problems. That's why we always have our handy dandy calculator. But what if you don't? You wouldn't be always carrying your calculating device everywhere, would you?

If you want to answer math problems in a snap, here's a useful math shortcut that you might wanna try before you become too dependent on calculators.. (To the point that you'd actually type 1 + 1 when the answer is already obvious).


Multiplying a number by 9.

169 X 9 is equal to? Something. You stare at the numbers with annoyance. But seriously, try and calculate it by yourself. You can write it down on a paper or mentally solve it. NO CALCULATORS!

Done? Okay. Here's the trick. You can actually solve this by using the number 10. How?
Watch:

169 X 10 = 1690
1690 - 169 = 1521

Try checking if it has the same answer as 169 x 9. It's the same, isn't it? So how did it happen?

Remember that 10 - 1 is 9.
So, basically: 169 x 9 == 169 x (10 - 1)
And we all know dividing any number to 10 is easy.

Well, it's faster if you like subtraction and subtraction is much easier than multiplication, right?


There'll be more Mathematical Solutions so stay tuned :3