Simple Math trick : Multiplying by 9, or 99, or 999

Multiplying by 9 is really multiplying by (10-1).

So, 9x9 is just 9x(10-1) which is 9x10-9 which is 90-9 or 81.

Let us try another example: 56x9 = 56x10-56 = 560-56 = 504.
Isn't it simple enough.


To multiply by 99, you multiply by 100-1.

So same principle, 56x99 = 56x(100-1) = 5600-56 = 5544.

Same applicable for 999,9999 and so on.