When you first began to learn addition and subtraction facts, you were faced with problems like 1 + 2 = __ or 1 + __ = 3 In algebra, we give a name to the blank. We call it a variable and we represent it with a letter or word or other symbol. 1 + 2 = x or 1 + y = 3 You use a variable wherever you want to represent an unknown quantity. You use the same variable whenever you want to represent the same number, and a different variable when you want to represent a different number.

__Example__x + x = 6 (a number added to itself is 6) x + y = 9 (the sum of two numbers is 9)