## Saturday, October 3, 2009

### Math tip I learned in grade school

Multiplying two double digit number is hard for grade schools, little bit hard for high schools and not so hard for college. But still, it takes time solving if not using a calculator. But luckily, I learned something great when I was in grade school for multiplying numbers greater than 10 and less than 20, that is 11, 12, 13, 14, 15, 16, 17, 18, 19.

For example, 14 x 17.

normal solving:
2
14
x 17
98
14
238

You will see that solving 14 x 17 occupies 6 lines, and can consume time.

But with the use of the shortcut I learned, the time and the lines will surely decrease.

with the shortcut:
2
14
x 17
238

"Obtained it by multiplying 4 and 7, then get 28. That first step is like the first step of normal multiplying. You put 8, then carry 2. Then, (this will be the shortcut part) instead of multiplying 7 by 1 (or 1 by 7), you will just add 14 (the number above) to 7 (the first digit below) and you will get 21. After it, just add the carry (which is 2) and get 23. Write it and then you will get 238."

Yes, shortcut it is! Nice huh?

So for the step by step instructions:
1. Multiply the first digits. Then carry the excess.
2. Add the number above by the first digit below. If there is a carry, add it also.
Voila! Multiplying two digit number in just 2 steps.

NOTE: Only applicable to numbers above 10 and numbers below 20.

Sorry for the poor formatting of the numbers, blogger doesn't allow me to format it nicely.