7th Grade Math

Add and Subtract Fractions

PART A BDE

2

C

Multi-Part

Lesson

Get ConnectED

GLE 0706.2.2

Understand and work with

the properties of and

operations on the system of

rational numbers.

SPI 0706.2.1 Simplify

numerical expressions

involving rational numbers.

Also addresses GLE 0706.1.8,

SPI 0706.2.3.

Main Idea

Add and subtract

fractions with unlike

denominators.

Vocabulary

unlike fractions

Add and Subtract

Unlike Fractions

MEASUREMENT The table shows the

fractions of one hour for different minutes.

1. Write each fraction in simplest form.


2. What fraction of one hour is equal to
   the sum of 15 minutes and 20 minutes?
   Write in simplest form.


3. Explain why ^1
   6
   hour + ^1
   3
   hour =
   _^1
   2
   hour.


4. Explain why ^1
   12
   hour + ^1
   2
   hour =
   _^7
   12
   hour.

Before you can add two unlike fractions, or fractions with different

denominators, one or both of the fractions must be renamed so that

they have a common denominator.

Add or Subtract Unlike Fractions

To add or subtract fractions with different denominators,

• Rename the fractions using the least common denominator (LCD).


• Add or subtract as with like fractions.


• If necessary, simplify the sum or difference.

Add Unlike Fractions

Find _^1

2

+ _^1

4

.

Method 1 Use a model.

+

1

2

1

4

1

4

1

4

1

4

1

4

1

4

1

2

3

4

1

4

1

4

1

4

fractio

Number of

Minutes

Fraction of

One Hour

1 _ 601

5 _ 605

10 _^1060

15 _^1560

20 _^2060

30 _^3060

146 Rational Numbers

V

u

139_156_C3L2_895130.indd 146 12/31/09 12:37 PM