Pre-Algebra Demystified

In order to find the unknown in a proportion, cross multiply and then solve
the equation for the unknown: i.e., divide by the number that is in front of the
variable.

EXAMPLE
Find the value of x:

x

5

¼

36

45

SOLUTION

x

5

¼

36

45

45x¼ 5 36 Cross multiply

45x¼ 180

45 x

45

¼

180

45

Divide

x¼ 4

EXAMPLE

Find the value of x:

24

32

¼

x

4

SOLUTION

24

32

¼

x

4

24  4 ¼32x Cross multiply

96 ¼32x

96

32

¼

32 x

32

Divide

3 ¼x

EXAMPLE

Find the value of x:

x

15

¼

26

75

CHAPTER 8 Ratio and Proportion 155