# Cross multiplying is a strategy for finding the missing part of a set of equivalent fractions. - PowerPoint PPT Presentation

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Cross multiplying is a strategy for finding the missing part of a set of equivalent fractions. The letter a is supposed to represent the number you don’t know yet. It is called a variable. 1. 5. =. 2. a. Use that brain in your head: If 10 is 1 times some number,

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Cross multiplying is a strategy for finding the missing part of a set of equivalent fractions.

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#### Presentation Transcript

Cross multiplying is a

strategy for finding

the missing part of a

set of equivalent

fractions.

The letter a is supposed

to represent the number you don’t know yet. It is called a variable.

1

5

=

2

a

If 10 is 1 times some number,

what is that number?

The letter a is supposed

To represent the number

You don’t know yet. It is called a variable.

Cross multiplying is a

strategy for finding

the missing part of a

set of equivalent

fractions.

1

5

=

2

a

2 x 5

= 1 x a

= 1 x a

10

Yes. Since 10 = 1 x 10,

the variable a in this

case is 10.

1

5

=

2

a

10

2 x 5

= 1 x a

= 1 x a

10

If 84 is three times some number, then

84 ÷ 3 will reveal

the missing amount.

3

12

=

7

a

7 x 12

= 3 x a

84

= 3 x a

If 84 is three times some number, then

84 ÷ 3 will reveal

the missing amount.

2

8

8 4

3

6

3

12

2

4

=

2

4

7

a

0

7 x 12

= 3 x a

84

= 3 x a

If 84 is three times some number, then

84 ÷ 3 will reveal

the missing amount.

2

8

8 4

3

6

3

12

2

4

=

2

4

7

a

28

0

7 x 12

= 3 x a

84

= 3 x a

(6 x 2) +3=15

6

0

6

0

15

b

__

__

25

1500

=

3

25

100

15

0

0

0

25 x b

15 x 100

=

0

1,500 ÷ 25

=

b

0

6

0

=

b

66.6

6

6

6

8

n

12

8 0 0

0

=

72

12

100

8

0

72

800

12 n

=

8

0

n

800 /12

=

7 2

n

66.6 =

A LOT OF STEPS!

Soon you will

know how to solve

even harder problems!