Adding and Subtracting Unlike Fractions

Lesson 4-3

Rewrite the problem with equivalent fractions

• List the multiples of both denominators.• Find the least common multiple (LCM).• Write new fractions with the LCM as the

new denominator.• Find the factor you multiply by to get

from your original denominator to your new denominator.

• Use that same factor, and multiply it by your original numerator to get a new numerator.

WHAT DOES THAT MEAN?Let’s illustrate the steps with an example.

34

+ 16

34

+ 16

Multiples of 4: 4, 8, 12, 16, 20

Multiples of 6: 6, 12, 18, 24, 30

+12 12

x 3 9 x 22

1211

Example 2

9

1025

10, 20, 30, 40, 50

5, 10, 15, 20, 25

10 10

x 1

9x 2

4 =105

= 12

Homework Time!