Fraction Multiplicatio
nAnd Cancelation
Fraction Multiplication• Here are some
fraction multiplication problems
• Can you tell how to multiply fraction from these examples?
4 1 45 7 35
6 4 245 10 50
21
10
7
5
3
2
3 5 154 12 48
1 1 13 3 9
2 5 103 1 3
Multiplication• Multiply numerator by numerator• And denominator by denominator
2 5 103 1 3
1 2 1 2
1 2 1 2
N N N ND D D D
Try some.• Multiply the following:
4 29 3
1 53 8
2 43 5
5 58 8
Answers• Multiply the following:
4 2 89 3 27
1 5 53 8 24
2 4 83 5 15
5 5 258 8 64
Mixed Numbers• Because of the order of operations,• Mixed numbers cannot be multiplied as is• Change mixed numbers to improper
fractions, then multiply.
8
51
5
23
17 135 8
17 13 2215 8 40
221 40 5 with a remainder of 21
215
40
Try some• Change any whole or mixed numbers
to improper.• Multiply straight across.• Simplify answers
21 7
5
18
5
Answers• Change any whole or mixed numbers
to improper.• Multiply straight across.• Simplify answers
2 7 7 49 41 7 9
5 5 1 5 5
1 1 8 8 38 1
5 5 1 5 5
Cancelling
Reduce before you multiply
Canceling• Reducing before mutiplying is called
canceling.
• ICK! Instead think the following in your head.
1120
300
35
12
32
25
25 12 25 12 5 5 4 332 35 32 35 8 4 7 5
5 5 4 3 5 3 158 4 7 5 8 7 56
Canceling on paper• Rules: One factor from
any numerator cancels with like factor from the denominator.
12
15
20
9
21
16
4
16 921 20
15
3
1216
4
4
921 20
15
3
31216
4
4
921 20
15
3
1
312
1
164
1
4
921
120
15
31
312
1
164
1
217
9
3
4120
15
31
312
1
37
Try one• Say “--- goes into ____ this many times.”• As you cross each number out and write
what is left after canceling above the number.
10
1
3
5
Answer• Say “--- goes into ____ this many times.”• As you cross each number out and write
what is left after canceling above the number.
51
13 10
2
56
Try one more• Make whole and mixed numbers improper• Cancel if you can• Multiply Numerators and denominators
straight across.• Simplify
415
14
2
14
21
10
Answer• Make whole and mixed numbers improper• Cancel if you can• Multiply Numerators and denominators
straight across.• Simplify
10 1 144 4
21 2 1510 9 14 4
821 2 15 1
