# Addition Equations up to Three Digits

One of the basic concepts of algebra is the equation. The most important thing to know about an equation is that everything on one side of the equal sign (=) must equal everything on the other side of the equal sign.

A simple equation with x as the variable:

x + 5 = 7

x= ?

x = 2 because 2 + 5 = 7.

###### Solving an Equation

We can tell by looking at it in the equation above that x = 2, but this is not always the case. Sometimes we need to work harder to solve the equation.

We can solve the same number by adding or subtracting both sides of the equation. We know this is okay because as long as we do the same on both sides of the equation, the equation doesn’t change.

Let’s try solving it by adding or subtracting both sides for this simple example

x + 5 = 7

We want to find what x equals, so we have to find x by itself on one side of the equation. If we subtract 5 from the left side, x will be by itself. According to our previous rule, we should do the same to the right side.

(x + 5) – 5 = (7) – 5

x = 2