today we will review “multiplying & dividing fractions”

CONFIDENTIAL 1

Today we will review “Multiplying & Dividing Fractions”

CONFIDENTIAL 2

Let’s Warm up:.

1) ¾ + ¼ = 2) 3/5 – 1/4 =

3) 5/6 – 2/5 = 4) ½ + ¾ - ¼ =

CONFIDENTIAL 3

Estimating Products

Estimate using Compatible Numbers These are numbers that are easy to divide mentally Estimate ¼ x 13 ¼ x 13 means ¼ of 13 Find a number close to13 that is a multiple of 4. ¼ x 13 ¼ x 12 ¼ x 12 = 3 So, ¼ x 13 is about 3.

12 and 4 are compatible numbers since 12 ÷ 4 = 3

12 ÷ 4 = 3

CONFIDENTIAL 4

Estimating Products

Your Turn! Estimate 2/5 x 11

CONFIDENTIAL 5

Estimating Products

Estimate by Rounding to 0, ½, or 1. Estimate 1/3 x 7/8

1/3 x 7/8 ½ x 1 ½ x 1 = ½ So, 1/3 x 7/8 is about ½.

0 1/2 1

1/3 7/8

1/3 is about 1/2 7/8 is about 1

CONFIDENTIAL 6

Estimating Products

Your Turn! Estimate 5/8 x 9/10

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Estimating Products

Estimating with Mixed Numbers 11 ¾ x 8 1/6 Round each number to the nearest whole number 11 ¾ x 8 1/6 12 x 8 = 96

Round 11 ¾ to 12 Round 8 1/6 to 8

CONFIDENTIAL 8

Multiplying Fractions

To multiply fractions, multiply the numerators and multiply the denominators a x c = a x c

b d b x d where b and d are not 0 2 x 1 = 2 x 1 = 2

5 2 5 x 2 10

CONFIDENTIAL 9

Multiplying Fractions

Your Turn Find 1/3 x 1/4

CONFIDENTIAL 10

Multiplying Fractions

Multiplying Fractions and Whole Numbers First write the whole number as a fraction Example; Find 3/5 x 4 3/5 x 4 = 3/5 x 4/1

= 3 x 4

5 x 1

= 12 or 2 2/5

5

Write 4 as 4/1

Multiply

Simplify

CONFIDENTIAL 11

Multiplying Fractions

Your Turn 2/3 x 6

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Multiplying Fractions

Simplify before Multiplying Find ¾ x 5/6 ¾ x 5/6 = 3 x 5 = 3 x 5

4 x 6 4 x 6

= 5

8

1

2

The numerator 3 and denominator 6

have a common factor 3

Divide both the numerator and the denominator by 3

CONFIDENTIAL 13

Multiplying Fractions

Find 5/6 x 9/10

CONFIDENTIAL 14

Multiplying Fractions

Evaluate Expressions Evaluate ab if a = 2/3 and b = 3/8 ab = 2/3 x 3/8

= 2 x 3

3 x 8

= 1

4

Replace a with 2/3 and b with 3/8

The GCF of 2 and 8 is 2. The GCF of 3 and 3 is 3. Divide both the numerator and denominator

by 2 and then by 3.

1

1

1

4

CONFIDENTIAL 15

Multiplying Fractions

Evaluate 3 c if c = 2

4 5

CONFIDENTIAL 16

Multiplying Mixed Numbers

To multiply mixed numbers, write the mixed numbers as improper fractions

Then multiply as with fractions Find ¼ x 4 4/5

5

11

5

654

2415

24

4

15

44

4

1

Divide 24 and 4 by their GCF, 4

1

4

CONFIDENTIAL 17

Multiplying Mixed Numbers

Your Turn Find 2/3 x 2 1/2

CONFIDENTIAL 18

Multiplying Mixed Numbers

Your Turn Find 2 ½ x 2 ¼

CONFIDENTIAL 19

Dividing Fractions

To divide by a fraction, multiply by its reciprocal

Any two numbers whose product is 1 are called reciprocals. 5 x 1/5 = 1; so the reciprocal of 5 is 1/5

To find the reciprocal of a fraction, invert the fraction. That is, switch the numerator and denominator.

Reciprocal of 2/3 is 3/2

0 d and c,b, where, c

d

b

a

d

c

b

a

CONFIDENTIAL 20

Dividing Fractions

Find 1/8 ÷ 3/4

rs.DenominatoMultiply .numeratorsMultiply 6

1

4 GCF by the 4 and 8 Divide 38

41

3

4 reciprocal by theMultiply

3

4

8

1

4

3

8

1

2

1

CONFIDENTIAL 21

Dividing Fractions

Your Turn Divide ¼ ÷ 3/8

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Dividing Mixed Numbers

1. Write mixed numbers as improper fractions

2. Multiply by the reciprocal

3. Simplify

7

13or

7

22

2 GCF by the 4 and 2 Divide 7

4

2

11

reciprocal by theMultiply 7

4

2

11

fractionsimproper as numbers mixed Write4

7

2

11

4

31

2

15

4

31

2

15 Find

2

1

CONFIDENTIAL 23

Dividing Mixed Numbers

Your Turn Divide. Write in simplest form.

3

12

5

14

CONFIDENTIAL 24

Let’s take a break!

CONFIDENTIAL 25Title: Format: WebEx Web BrowserDouble-click to edit

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Assessment

1. Estimate 1/8 x 15

2. Estimate ¾ x 21

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Assessment

3. Multiply. Write in simplest form. 1/8 x ½

4. Multiply. Write in simplest form. 4/5 x 10

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Assessment

5. Multiply. Write in simplest form.

6. Multiply. Write in simplest form.

8

32

2

1

3

2

2

11

CONFIDENTIAL 29

Assessment

7. Divide. Write in simplest form.

8. Divide. Write in simplest form.

2

1

4

1

3

1

6

5

CONFIDENTIAL 30

Assessment

9. Divide. Write in simplest form.

10. Divide. Write in simplest form.

22

13

7

2

5

13

CONFIDENTIAL 31

Good Job!

You have learned a lot today!!!