Algebra uses letters (like x or y) or other symbols in place of values, and then plays with them using special rules.

Example: **x + 3 = 7**

"x" is used in place of a value we don't know yet and is called the "unknown" or the "variable".

In this case the value of "x" can be found by subtracting 3 from both sides of the equal sign like this:

Start with: x + 3 = 7

Subtract 3 from both sides: x + 3 − 3 = 7 − 3

Calculate: x + 0 = 4

Answer: x = 4