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We need to say b 0 , c 0 and d 0 to be sure we don’t divide by zero.

Divide, and write the answer in simplified form: 2 5 ÷ ( 3 7 ) .

Solution

2 5 ÷ ( 3 7 )
Multiply the first fraction by the reciprocal of the second. 2 5 ( 7 3 )
Multiply. The product is negative. 14 15
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Divide, and write the answer in simplified form: 3 7 ÷ ( 2 3 ) .

9 14

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Divide, and write the answer in simplified form: 2 3 ÷ ( 7 5 ) .

10 21

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Divide, and write the answer in simplified form: 2 3 ÷ n 5 .

Solution

2 3 ÷ n 5
Multiply the first fraction by the reciprocal of the second. 2 3 · 5 n
Multiply. 10 3 n
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Divide, and write the answer in simplified form: 3 5 ÷ p 7 .

21 5 p

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Divide, and write the answer in simplified form: 5 8 ÷ q 3 .

15 8 q

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Divide, and write the answer in simplified form: 3 4 ÷ ( 7 8 ) .

Solution

3 4 ÷ ( 7 8 )
Multiply the first fraction by the reciprocal of the second. 3 4 · ( 8 7 )
Multiply. Remember to determine the sign first. 3 · 8 4 · 7
Rewrite to show common factors. 3 · 4 · 2 4 · 7
Remove common factors and simplify. 6 7
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Divide, and write the answer in simplified form: 2 3 ÷ ( 5 6 ) .

4 5

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Divide, and write the answer in simplified form: 5 6 ÷ ( 2 3 ) .

5 4

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Divide, and write the answer in simplified form: 7 18 ÷ 14 27 .

Solution

7 18 ÷ 14 27
Multiply the first fraction by the reciprocal of the second. 7 18 · 27 14
Multiply. 7 · 27 18 · 14
Rewrite showing common factors. .
Remove common factors. 3 2 · 2
Simplify. 3 4
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Divide, and write the answer in simplified form: 7 27 ÷ 35 36 .

4 15

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Divide, and write the answer in simplified form: 5 14 ÷ 15 28 .

2 3

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Key concepts

  • Equivalent Fractions Property
    • If a , b , c are numbers where b 0 , c 0 , then a b = a c b c and a c b c = a b .
  • Simplify a fraction.
    1. Rewrite the numerator and denominator to show the common factors. If needed, factor the numerator and denominator into prime numbers.
    2. Simplify, using the equivalent fractions property, by removing common factors.
    3. Multiply any remaining factors.
  • Fraction Multiplication
    • If a , b , c , and d are numbers where b 0 and d 0 , then a b c d = a c b d .
  • Reciprocal
    • A number and its reciprocal have a product of 1 . a b b a = 1
    • Opposite Absolute Value Reciprocal
      has opposite sign is never negative has same sign, fraction inverts
  • Fraction Division
    • If a , b , c , and d are numbers where b 0 , c 0 and d 0 , then
      a b + c d = a b d c
    • To divide fractions, multiply the first fraction by the reciprocal of the second.

Practice makes perfect

Simplify Fractions

In the following exercises, simplify each fraction. Do not convert any improper fractions to mixed numbers.

Multiply Fractions

In the following exercises, use a diagram to model.

In the following exercises, multiply, and write the answer in simplified form.

7 12 ( 8 21 )

2 9

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( 14 15 ) ( 9 20 )

21 50

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( 63 84 ) ( 44 90 )

11 30

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( 33 60 ) ( 40 88 )

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Find Reciprocals

In the following exercises, find the reciprocal.

Fill in the chart.

Opposite Absolute Value Reciprocal
7 11
4 5
10 7
−8
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Fill in the chart.

Opposite Absolute Value Reciprocal
3 13
9 14
15 7
−9


A table is shown with four columns and five rows. The first row reads Number, Opposite, Absolute Value, and Reciprocal. The second row reads negative three thirteenths, three thirteenths, three thirteenths, negative thirteen thirds. The third row reads nine fourteenths, negative nine fourteenths, nine fourteenths, and fourteen ninths. The fourth row reads fifteen sevenths, negative fifteen sevenths, fifteen sevenths, and seven fifteenths. The last row reads negative nine, nine, nine, negative one ninth.

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Divide Fractions

In the following exercises, model each fraction division.

In the following exercises, divide, and write the answer in simplified form.

5 6 ÷ ( 5 6 )

1

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7 18 ÷ ( 14 27 )

3 4

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12 r 25 ÷ 18 s 35

14 r 15 s

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2 5 ÷ ( −10 )

1 25

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1 2 ÷ ( 3 4 ) ÷ 7 8

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Everyday math

Baking A recipe for chocolate chip cookies calls for 3 4 cup brown sugar. Imelda wants to double the recipe.

How much brown sugar will Imelda need? Show your calculation. Write your result as an improper fraction and as a mixed number.

Measuring cups usually come in sets of 1 8 , 1 4 , 1 3 , 1 2 , and 1 cup. Draw a diagram to show two different ways that Imelda could measure the brown sugar needed to double the recipe.

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Baking Nina is making 4 pans of fudge to serve after a music recital. For each pan, she needs 2 3 cup of condensed milk.

  1. How much condensed milk will Nina need? Show your calculation. Write your result as an improper fraction and as a mixed number.
  2. Measuring cups usually come in sets of 1 8 , 1 4 , 1 3 , 1 2 , and 1 cup. Draw a diagram to show two different ways that Nina could measure the condensed milk she needs.

  • 4 2 3 = 8 3 = 2 2 3
  • Answers will vary.

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Portions Don purchased a bulk package of candy that weighs 5 pounds. He wants to sell the candy in little bags that hold 1 4 pound. How many little bags of candy can he fill from the bulk package?

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Portions Kristen has 3 4 yards of ribbon. She wants to cut it into equal parts to make hair ribbons for her daughter’s 6 dolls. How long will each doll’s hair ribbon be?

1 8 yard

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Writing exercises

Explain how you find the reciprocal of a fraction.

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Explain how you find the reciprocal of a negative fraction.

Answers will vary.

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Rafael wanted to order half a medium pizza at a restaurant. The waiter told him that a medium pizza could be cut into 6 or 8 slices. Would he prefer 3 out of 6 slices or 4 out of 8 slices? Rafael replied that since he wasn’t very hungry, he would prefer 3 out of 6 slices. Explain what is wrong with Rafael’s reasoning.

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Give an example from everyday life that demonstrates how 1 2 · 2 3 is 1 3 .

Answers will vary.

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Self check

After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.

.

After reviewing this checklist, what will you do to become confident for all objectives?

Practice Key Terms 2

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Source:  OpenStax, Prealgebra. OpenStax CNX. Jul 15, 2016 Download for free at http://legacy.cnx.org/content/col11756/1.9
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