Adding and Subtracting Unlike Fractions

3.6

To add and subtract fractions with unlike denominators, first find a common denominator

using one of these methods:

Method 1 Find a common denominator by multiplying the two denominators.

Method 2 Find the least common denominator (LCD) of the

denominators. (Cake Method)

Steps

• Find LCD or CD• Write equivalent fractions: Multiply the

fraction by a value of 1 in order to get the LCD or CD

• Add or subtract the numerators• Reduce

Write in Simplest form:

• LCD: 18

• Rename Fractions:

• Add the numerators:

5 1

9 6

5 2 10

9 2 18

1 3 3

6 3 18

10 3

18 18

10 3

18

7

18

Write the answer in simplest form.

3 2 4 5

2015

2320

20+ 8

3120

55 4

4Find a common denominator: 4(5) = 20.

Multiply by fractions equal to 1.

Rewrite with common denominators.

Add numerators. Keep the denominator.

Rewrite as a mixed number.

Write in Simplest Form:5 1

5 26 4

35 9

6 4

2

2 3

3

70 27

12 12

97

121

812

Find the perimeter of the figure below.

21 in.3

11 in.4

12 in.2

2 131 141 22

+

12

81

12

31

12

62

1712

4

5112

4 5512

44

33

66

First, work with the fractions.Then, work with the whole numbers.Last, simplify.

Vickie has cups of shredded cheese to put in her enchilada casserole and ¾ cup of cheese for the top. If she has 3 cups of cheese in all, how much cheese will

she have left?

21

3

2 33 1

3 4

5 33

3 4

4 5 3 33

4 3 3 4

20 93

12 12

293

1212 29

312 12

36 29

12 12

7

12

Homework:

• Page 129 (14-46) even