cryptarithmetic

How come I've never heard of this before???

You make a arithmetic problem out of letters which have associated number values, and make a cool phrase like this. You can try to decipher this one:

SEND+MORE=MONEY

or put this way

SEND

+MORE

-----

MONEY

so, since the letters are all digits from 0-9, and we know that S + M creates a carry, that carry (M) must be 1. You can use logic and modular arithmetic to derive the values for the remainder of the letters. Cool...