Transcript Fraction Multiplication & Division Review

Fraction Multiplication and
Division
Review Topic 7
Look at the following examples. Decide
what the rule is for multiplying fractions.
Examples: 2/3 x 1/5 = 2/15
9
4/5 x 3/ 4 =12/20=3/5 3 3
,
 
4 4 16
5
5 3 15 7
3    1
8
8 1 8
8
Rule
Notice: Fraction numbers must be
written as the ratio of two integers to be
multiplied.
a c ac
 
b d bd
Thus to multiply 2 ½ x 1 ¾ x 12
First change the mixed numbers to
improper fractions 5/2 x 7/4 x12/1
to get 420/8
This can be reduced to 52 ½.
Cancellation
One other step can save time.
Canceling reduces the answer before
you multiply the numbers.
3
3
15 7 12 15
7 12
3  7  3 63
  
 

 63
10
2 4 25
2
4
2

1

5
10
25
5
1
Fraction Division
To divide fractions, invert the second
fraction and multiply.
2/3  ½ = 2/3 x 2/1 = 4/3 = 1 1/3.
Rule:
a c a d ad
  x 
b d b c bc
Things to Remember
Notice: DON”T cancel until after the
divisor (second number) is inverted.
For word problems, be very careful
which number to write first in the
problem.
The thing being split, cut apart, or sorted
goes first.
Example:
1
1 10 5 10 2 2 2 4 1
3  2        1
3
2 3 2 3 5 3 1 3 3
Steps
Change to improper
Invert and Multiply
Cancel
Multiply
Simplify