fraction multiplication

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