In this thread you all can post interesting math helper things and ways to find out answers to problems that have been discovered in the past. My favorite one is like this, and was discovered by Pythagoras. I find this most fascinating:

Ever hear of the quick way to multiply 2-digit numbers by eleven?

Provided that the sum of the 2 integers that make up the 2-digit number is less than 10, all you have to do is add them up and stick the sum in between them...

12 * 11 = 132 (1 + 2 = 3, put between the 1 and the 2)

72 * 11 = 792 (7 + 2 = 9, put between the 7 and the 2)

There's such a fantastic mystical character to numbers... gotta love 'em!

Anyone else who has more please post them, these are so fun and interesting.