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:  5 9  1 6 • LCD: 18 • Rename Fractions:  9 5 2 2  10 18 6 3 • Add the numerators:  10  3 18 18  18 3 18   7 18

Write the answer in simplest form.

  5 5 4  2 5   4 Find a common denominator: 4(5) = 20.

Multiply by fractions equal to 1.

15 20

+

23 20 8 20  1 3 20 Rewrite with common denominators.

Add numerators. Keep the denominator.

Rewrite as a mixed number.

Write in Simplest Form:

2 2 5 5 6  35 6  2 1 4    70  9 4 27  12 12  3 3 97 12  1 8 12

Find the perimeter of the figure below.

2 3 1 2

First

, work with 1 4

+

1 2 3 1 1 2 4 1 2   6   3 3 4      the fractions.

Then

, work with the whole numbers.

Last

, simplify.

1 8 12 1 3 12 2 6 12 4 17 12 4  1 5 12  5 5 12

1 2 Vickie has cups of shredded cheese to put in her 3 enchilada casserole and ¾ cup of cheese for the top. If she has 3 cups of cheese in all, how much cheese will 3 3   1 2 3 5  3 she have left? 3  4 3 4 3  4 4  5 3  3 3  3 4 3  20 12  9 12 3  29 12 3  12 12 36   29 12  29 12 12 7 12

Homework:

• Page 129 (14-46) even