Example 4

9

7

–

5

3

=

?

The fractions have unlike denominators. First, find the Least Common Denominator and rewrite the fractions with the common denominator.

LCD(9/7, 5/3) = 21

Multiply both the numerator and denominator of each fraction by the number that makes its denominator equal the LCD. This is basically multiplying each fraction by 1:

9

7

x

3

3

–

	5

	3

x

	7

	7

27

21

–

35

21

=

	-8

	21