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Fraction Multiplication. And Cancelation. Fraction Multiplication. Here are some fraction multiplication problems Can you tell how to multiply fraction from these examples?. 14. 14. 14. 14. 34. __. __. __. __. __. - PowerPoint PPT Presentation
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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
Recall that multiplication by a whole number can be represented as repeated addition. For example, 4 • 5 = 5 + 5 + 5 + 5. You can multiply a whole number by a fraction using the same method.
++ =
3 • =14__ 1
4__ 1
4__ 1
4__ 3
4__++ =
31
__ 14
__ 3 • 11 • 4
______ 34
__•
There is another way to multiply with fractions. Remember that a whole number can be written as an improper fraction with 1 in the denominator. So 3 = .3
1__
= = Multiply numeratorsMultiply denominators
Notice that when you multiply a proper fraction and a number greater than 1, the product is between the factors.
1
3__1
4__
1
4__ 1
3__
1
4__ 1
3__
• =1
12__
One way to find of is to make a model.
Find of .
Multiplying Fractions
3
1
2
1
3
1
2
1of
6
1
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 multiplying 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
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