Transcript Add/Subtract Unlike Fractions

Add/Subtract Unlike Fractions
7th Grade Math
Lesson Objective:
Students will add and subtract fractions with unlike
denominators.
Vocabulary
 Unlike Fractions
 Fractions with different denominators
Steps
 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 1
 Find ½ + ¼
1

2
1
4
1x2
LCD  4

1

2x2
4
2
21
4

1
4

4

3
4
Add Unlike Fractions 2
 Find 9/10 + (-1/2)
 1
    LCD  10
10  2 
9
 1 x 5
 

10  2 x 5 
9
4
2
 5  9  (-5)
or
 


5
10  10 
10
10
9
Add Unlike Fractions - Practice
 Add. Write in simplest form.
 4
    
6  9
5
1

6

3

8
2
3

5
6

Subtract Unlike Fractions 1
 Find 2/3 – 1/2.
2

3
1
LCD  6
2
2x2

1x3
3x2
2x3
4
43
6

3
6

6


1
6
Subtract Unlike Fractions 2
 Find 1/2 – (-2/5)
 2
    LCD  10
2  5
1
 2 x 2
 

2 x 5  5 x 2
1 x5
9
 4  5  (-4)
 


10  10 
10
10
5
Subtract Unlike Fractions - Practice
 Subtract. Write in simplest form.
 1
   
8  4
3
7

12

5

6
7
10

2
5

Real World Example
 Cassandra cuts 5/16 inch off the top of a photo
and 3/8 inch off the bottom. How much shorter
is the total height of the photo now?
5

16
5
16
5
3
LCD  16
8

3x 2

8x2
6 5  6 11



inch
16 16
16
16
Real World Example - Practice
 A bucket was 7/8 fill with soapy water. After
washing the car, the bucket was only ¼ full. What
part of the water was used?