Transcript Silly Monster

Here are some fraction
multiplication problems
5
Can you tell how to
multiply fraction from
these examples?
2

3
5

7
1
3

1
3
2
10
3
21

4


5
1
1
7

3
1
4
9
6
5

4
10

4

35
10
3

5
12

15
48
24
50
Fraction Multiplication
Multiply numerator by numerator
And denominator by denominator
2
3
N1
D1


5
1
N2
D2


10
3
N1  N 2
D1  D 2
Multiplication
Try some.
Multiply the following:
2
3

4
5
4

9
1
3

5
8


2
3

5
8

5
8

Answers
Multiply the following:
2
3

4
5

8
4
15
1
3
9

5
8


2
3

8
27
5
5
24
8

5
8

25
64
Mixed Numbers
Because of the order of operations,
Mixed numbers cannot be multiplied as is
Change mixed numbers to improper fractions, then
multiply.
3
2
5
17
5

13
8

1
5

8
17
5

13
8

221
40
221  40  5 w ith a rem ain der of 21
5
21
40
Try some
1
2
5
7 
1
5
8 
Change any whole or mixed numbers to improper.
Multiply straight across.
Simplify answers
Answers
Change any whole or mixed numbers to improper.
Multiply straight across.
Simplify answers
1
2
5
1
5
7 
8 
7
5
1
5


7
1
8
1
49


5
8
5
 9
1
3
5
4
5
Canceling
Reducing before multiplying is called
canceling.
25

12
32
25
32

12
35

35

25  12
32  35
300
1120

5543
8475
Instead think the following in your head.
5543
8475

53
87

15
56
Rules: One factor from
any numerator cancels
with like factor from the
denominator.
11
44 44
16
1
6
16
16
16
16
21
3
99999

9

15
20
12
1
3
3 13
1
3
115
51 5
3
15
15






7
2
1
2
0
1
2
7
4
21 44420
12
21
20
1 20
12
221
1
20
133213
41
3
1
31
Canceling on paper
Say “--- goes into ____ this many times.”
As you cross each number out and write what is left
after canceling above the number.
5
3
Try one

1
10
Say “--- goes into ____ this many times.”
As you cross each number out and write what is left
after canceling above the number.
5
1
3
Answer

1
10

2
5
6
Make whole and mixed numbers improper
Cancel if you can
Multiply Numerators and denominators straight
across.
Simplify
10
21
4
1

2
Try one more
14
15
4
Make whole and mixed numbers improper
Cancel if you can
Multiply numerators and denominators straight
across.
Simplify
10
21
10
21
Answer
4

9
2
1
2


14
15
14
15

4
4
1
 8