7th Grade Math

Method 2 Use the LCD.

The least common denominator of _^12 and _^14 is 4.

_^1

2

+ _^1

4

= _^1 ×^2

2 × 2

+ _^1 ×^1

4 × 1

Rename using the LCD, 4.

= _^2

4

+ _^1

4

Add the fractions.

= _^34 Simplify.

Using either method, 21 + 41 = _^34.

Add. Write in simplest form.

a. ^16 + ^23 b. 109 + (^) (- ^12 ) c. 41 + 83
Subtract Unlike Fractions
Find ^23 - ^12.
Method 2 Use the LCD.
The least common denominator of ^23 and ^12 is 6.
32 - ^12 = ^23 × ×^22 - ^12 × ×^33 Rename using the LCD, 6.
= 64 - ^36 Subtract the fractions.
= _^16 Simplify.
Method 1 Use a model.

1

3

1

3

1 3 1 2 1 6

2

3

1

6

1

2

Check by adding _ 61 + _^12 = _ 61 + _^36 = _ 64 or _^23 ✓

Using either method, 32 - 21 = _^16.

Subtract. Write in simplest form.

d. _^58 - _^14 e. _^34 - _ 31 f. _ 21 - (- _^25 )

Check for Reasonableness

Estimate the difference in

Example 2.

_^2

3 -^

_^1

2 ≈^

_^1

2 -^

_^1

2 or 0.

Compare _ 61 to the estimate.

_^1

6 ≈ 0. So, the answer is

reasonable.

Lesson 2C Add and Subtract Fractions 147

139_156_C3L2_895130.indd 147 12/31/09 12:37 PM