A neat trick with the number 9:

Multiply 9 by any number you wish.

Lets say 9 * 36 = 324

Now add 3 + 2 + 4 = 9 !!!!!!

(Doesnt even have to be an integer)......

9 * 528.336 = 4755.024

Now add 4+7+5+5+0+2+4 = 27

Then add 2+7 = 9 !!!!!!!!!!!!!!

How COOOOOOL is that !!