Math tips, Math formulas

Multiply By 4




To quickly multiply by four, double the number and then double it again.

Often this can be done in your head.
 
 
Multiply By 5


To quickly multiply by 5, divide the number in two and then multiply it by 10. Often this can be done quickly in your head.
 
 
Finger Math:
 
9X Rule




To multiply by 9,try this:

(1) Spread your two hands out and place them on a desk or table in front of you.

(2) To multiply by 3, fold down the 3rd finger from the left. To multiply by 4, it would be the 4th finger and so on.

(3) the answer is 27 ... READ it from the two fingers on the left of the folded down finger and the 7 fingers on the right of it.



This works for anything up to 9x10!