Equations with Variables (Multiply and Divide)

In a variable equation we must either add or subtract the known number in the unknown expression. In the above equation the unknown expression is “X - 5”. As this shows the number “5” is being subtracted from “X” we must add 5 to 5 as follows:

X - 5 + 5

(NOTE: If 5 was being added in the first expression, then we would have to subtract 5 as follows: X + 5 – 5)

We must then do the equal math to the known express of “10” as follows:

10 + 5

The new equation will now look as follows:

X - 5 + 5 = 10 + 5

We now add 10 + 5 = 15 and that makes the value of “X” equal 15.

15 - 5 = 10 so X = 15

However, sometimes we are faced with a different variable such as 7X = 21. When we see this type of equation, we will need to divide the number in the unknown express with the number in the known expression and then multiply the number found in the unknown expression with the answer. For example:

7X = 21 becomes X = 21 ÷ 7
21 ÷ 7 = 3
7 x 3 = 21
X = 3