Pre-Algebra Demystified

SOLUTION

7x¼ 28

7 x

7

¼

28

7

Divide both sides by 7

x¼ 4

Check:

7x¼ 28

7 ð 4 Þ¼ 28

28 ¼ 28

An equation such as x 3 ¼15 can be solved by using themultiplication
principle.Both sides of an equation can be multiplied by the same non-zero
number without changing the nature of the equation.

EXAMPLE

Solve

x

3

¼15.

SOLUTION

x

3

¼ 15

1

3

1



x

3

¼ 15  3

1

x¼ 45

Check:

x

3

¼ 15

45

3

¼ 15

15 ¼ 15

As you can see, there are four basic types of equations and four basic
principles that are used to solve them. Before attempting to solve an equa-
tion, you should see what operation is being performed on the variable and
then use the opposite principle to solve the equation. Addition and sub-

CHAPTER 7 Expression and Equations 137