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4.7 Solve Equations with Fractions

Determine Whether a Fraction is a Solution of an Equation

As we saw in Solve Equations with the Subtraction and Addition Properties of Equality and Solve Equations Using Integers; The Division Property of Equality, a solution of an equation is a value that makes a true statement when substituted for the variable in the equation. In those sections, we found whole number and integer solutions to equations. Now that we have worked with fractions, we are ready to find fraction solutions to equations.

The steps we take to determine whether a number is a solution to an equation are the same whether the solution is a whole number, an integer, or a fraction.

Solve Equations with Fractions using the Addition, Subtraction, and Division Properties of Equality

In Solve Equations with the Subtraction and Addition Properties of Equality and Solve Equations Using Integers; The Division Property of Equality, we solved equations using the Addition, Subtraction, and Division Properties of Equality. We will use these same properties to solve equations with fractions.

We used the Subtraction Property of Equality in Example 2. Now we’ll use the Addition Property of Equality.

The next example may not seem to have a fraction, but let’s see what happens when we solve it.

Solve Equations with Fractions Using the Multiplication Property of Equality

Consider the equation x4=3. We want to know what number divided by 4 gives 3. So to “undo” the division, we will need to multiply by 4. The Multiplication Property of Equality will allow us to do this. This property says that if we start with two equal quantities and multiply both by the same number, the results are equal.

Let’s use the Multiplication Property of Equality to solve the equation x7=−9.

Solve Equations with a Coefficient of −1

Look at the equation y=15. Does it look as if y is already isolated? But there is a negative sign in front of y, so it is not isolated.

There are three different ways to isolate the variable in this type of equation. We will show all three ways in Example 7.

Solve Equations with a Fraction Coefficient

When we have an equation with a fraction coefficient we can use the Multiplication Property of Equality to make the coefficient equal to 1.

For example, in the equation:

34x=24

The coefficient of x is 34. To solve for x, we need its coefficient to be 1. Since the product of a number and its reciprocal is 1, our strategy here will be to isolate x by multiplying by the reciprocal of 34. We will do this in Example 8.

Translate Sentences to Equations and Solve

Now we have covered all four properties of equality—subtraction, addition, division, and multiplication. We’ll list them all together here for easy reference.

Subtraction Property of Equality:
For any real numbers a, b, and c,

if a=b, then ac=bc.
Addition Property of Equality:
For any real numbers a, b, and c,

if a=b, then a+c=b+c.
Division Property of Equality:
For any numbers a, b, and c, where c0

if a=b, then ac=bc
Multiplication Property of Equality:
For any real numbers a, b, and c

if a=b, then ac=bc

When you add, subtract, multiply or divide the same quantity from both sides of an equation, you still have equality.

In the next few examples, we’ll translate sentences into equations and then solve the equations. It might be helpful to review the translation table in Evaluate, Simplify, and Translate Expressions.

Key Concepts

  • Determine whether a number is a solution to an equation.
    1. Substitute the number for the variable in the equation.
    2. Simplify the expressions on both sides of the equation.
    3. Determine whether the resulting equation is true. If it is true, the number is a solution. If it is not true, the number is not a solution.
  • Addition, Subtraction, and Division Properties of Equality
    • For any numbers a, b, and c,
      if a=b, then a+c=b+c. Addition Property of Equality
    • if a=b, then ac=bc. Subtraction Property of Equality
    • if a=b, then ac=bc, c0. Division Property of Equality
  • The Multiplication Property of Equality
    • For any numbers ab and c, a=b, then ac=bc.
    • If you multiply both sides of an equation by the same quantity, you still have equality.

Section Exercises

Practice Makes Perfect

Determine Whether a Fraction is a Solution of an Equation

In the following exercises, determine whether each number is a solution of the given equation.

x25=110:

  1. x=1
  2. x=12
  3. x=12

y13=512:

  1. y=1
  2. y=34
  3. y=34
  1. ⓐ no
  2. ⓑ yes
  3. ⓒ no

h+34=25:

  1. h=1
  2. h=720
  3. h=720

k+25=56:

  1. k=1
  2. k=1330
  3. k=1330
  1. ⓐ no
  2. ⓑ yes
  3. ⓒ no

Solve Equations with Fractions using the Addition, Subtraction, and Division Properties of Equality

In the following exercises, solve.

y+13=43

m+38=78

m=12

f+910=25

h+56=16

h=23

a58=78

c14=54

c = −1

x(320)=1120

z(512)=712

z = −1

n16=34

p310=58

p=3740

s+(12)=89

k+(13)=45

k=715

5j=17

7k=18

k=187

−4w=26

−9v=33

v=113

Solve Equations with Fractions Using the Multiplication Property of Equality

In the following exercises, solve.

f4=−20

b3=−9

b = −27

y7=−21

x8=−32

x = −256

p−5=−40

q−4=−40

q = 160

r−12=−6

s−15=−3

s = 45

x=23

y=42

y = −42

h=512

k=1720

k=1720

45n=20

310p=30

p = 100

38q=−48

52m=−40

m = −16

29a=16

37b=9

b = −21

611u=−24

512v=−15

v = 36

Mixed Practice

In the following exercises, solve.

3x=0

8y=0

y = 0

4f=45

7g=79

g=19

p+23=112

q+56=112

q=34

78m=110

14n=710

n=145

25=x+34

23=y+38

y=2524

1120=f

815=d

d=815

Translate Sentences to Equations and Solve

In the following exercises, translate to an algebraic equation and solve.

n divided by eight is −16.

n divided by six is −24.

n6=−24;n=−144

m divided by −9 is −7.

m divided by −7 is −8.

m−7=−8;m=56

The quotient of f and −3 is −18.

The quotient of f and −4 is −20.

f−4=−20;f=80

The quotient of g and twelve is 8.

The quotient of g and nine is 14.

g9=14;g=126

Three-fourths of q is 12.

Two-fifths of q is 20.

25q=20;q=50

Seven-tenths of p is −63.

Four-ninths of p is −28.

49p=−28;p=−63

m divided by 4 equals negative 6.

The quotient of h and 2 is 43.

h2=43;h=86

Three-fourths of z is 15.

The quotient of a and 23 is 34.

a23=34;a=12

The sum of five-sixths and x is 12.

The sum of three-fourths and x is 18.

34+x=18;x=58

The difference of y and one-fourth is 18.

The difference of y and one-third is 16.

y13=16;y=16

Everyday Math

Shopping Teresa bought a pair of shoes on sale for $48. The sale price was 23 of the regular price. Find the regular price of the shoes by solving the equation 23p=48

Playhouse The table in a child’s playhouse is 35 of an adult-size table. The playhouse table is 18 inches high. Find the height of an adult-size table by solving the equation 35h=18.

30 inches

Writing Exercises

Example 6 describes three methods to solve the equation y=15. Which method do you prefer? Why?

Richard thinks the solution to the equation 34x=24 is 16. Explain why Richard is wrong.

Answers will vary.

Self Check

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

A self-assessment chart with 'I can...' statements related to solving equations with fractions, including determining solutions, using properties of equality, and translating sentences, with columns for confidence levels: Confidently, With some help, and No-I don't get it!
Figure 4.14

ⓑ Overall, after looking at the checklist, do you think you are well-prepared for the next Chapter? Why or why not?

Chapter Review Exercises

Visualize Fractions

In the following exercises, name the fraction of each figure that is shaded.

A circle is shown. It is divided into 8 equal pieces. 5 pieces are shaded.
A square is shown. It is divided into 9 equal pieces. 5 pieces are shaded.

59

In the following exercises, name the improper fractions. Then write each improper fraction as a mixed number.

Two squares are shown. Both are divided into four equal pieces. The square on the left has all 4 pieces shaded. The square on the right has one piece shaded.
Two circles are shown. Both are divided into two equal pieces. The circle on the left has both pieces shaded. The circle on the right has one piece shaded.

32=112

In the following exercises, convert the improper fraction to a mixed number.

5815

6311

5811

In the following exercises, convert the mixed number to an improper fraction.

1214

945

495

Find three fractions equivalent to 25. Show your work, using figures or algebra.

Find three fractions equivalent to 43. Show your work, using figures or algebra.

Answers may vary.

In the following exercises, locate the numbers on a number line.

58,43,334,4

14,14,113,−113,72,72

A number line is shown. Integers from negative 4 to 4 are labeled. Between negative 4 and negative 3, negative 7 halves is labeled and marked with a red dot. Between negative 2 and negative 1, negative 1 and 1 third is labeled and marked with a red dot. Between negative 1 and 0, negative 1 fourth is labeled and marked with a red dot. Between 0 and 1, 1 fourth is labeled and marked with a red dot. Between 1 and 2, 1 and 1 third is labeled and marked with a red dot. Between 3 and 4, 7 halves is labeled and marked with a red dot.

In the following exercises, order each pair of numbers, using < or >.

−1___25

−212___−3

>

Multiply and Divide Fractions

In the following exercises, simplify.

6384

90120

34

14a14b

8x8y

xy

In the following exercises, multiply.

25·813

13·127

47

29·(4532)

6m·411

24m11

14(−32)

165·158

6

In the following exercises, find the reciprocal.

29

154

415

3

14

−4

Fill in the chart.

OppositeAbsolute ValueReciprocal
513
310
94
−12

In the following exercises, divide.

23÷16

4

(3x5)÷(2y3)

45÷3

415

8÷83

518÷(b9)

52b

Multiply and Divide Mixed Numbers and Complex Fractions

In the following exercises, perform the indicated operation.

315·178

−5712·4411

26811

8÷223

823÷1112

8

In the following exercises, translate the English phrase into an algebraic expression.

the quotient of 8 and y

the quotient of V and the difference of h and 6

Vh6

In the following exercises, simplify the complex fraction

5845

89−4

29

n438

−156112

22

In the following exercises, simplify.

5+165

8·4523·12

736

8·7+5(810)9·36·4

Add and Subtract Fractions with Common Denominators

In the following exercises, add.

38+28

58

45+15

25+15

35

1532+932

x10+710

x+710

In the following exercises, subtract.

811611

1112512

12

45y5

3130730

1915

32(32)

1115515(215)

815

Add and Subtract Fractions with Different Denominators

In the following exercises, find the least common denominator.

13 and 112

13 and 45

15

815 and 1120

34,16,and510

60

In the following exercises, change to equivalent fractions using the given LCD.

13 and 15, LCD =15

38 and 56, LCD =24

924 and 2024

916 and 512, LCD =48

13,34 and 45, LCD =60

2060,4560 and 4860

In the following exercises, perform the indicated operations and simplify.

15+23

111223

14

91034

11361120

7790

2225+940

y1013

3y1030

25+(59)

411÷27d

14d11

25+(3n8)(29n)

(23)2(58)2

256225

(1112+38)÷(56110)

In the following exercises, evaluate.

y45 when

  1. y=45
  2. y=14
  1. 85
  2. 1120

6mn2 when m=34 and n=13

Add and Subtract Mixed Numbers

In the following exercises, perform the indicated operation.

413+913

1323

625+735

5811+2411

8111

358+378

9132041120

5110

23101910

211121712

113

86112911

Solve Equations with Fractions

In the following exercises, determine whether the each number is a solution of the given equation.

x12=16:

  1. x=1
  2. x=23
  3. x=13
  1. ⓐ no
  2. ⓑ yes
  3. ⓒ no

y+35=59:

  1. y=12
  2. y=5245
  3. y=245

In the following exercises, solve the equation.

n+911=411

n=511

x16=76

h(78)=25

h=5140

x5=−10

z=23

z = −23

In the following exercises, translate and solve.

The sum of two-thirds and n is 35.

The difference of q and one-tenth is 12.

q110=12;q=35

The quotient of p and −4 is −8.

Three-eighths of y is 24.

38y=24;y=64

Chapter Practice Test

Convert the improper fraction to a mixed number.

195

Convert the mixed number to an improper fraction.

327

237

Locate the numbers on a number line.

12,123,−234, and 94

In the following exercises, simplify.

520

14

18r27s

13·34

14

35·15

−36u(49)

16u

−5712·4411

56÷512

−2

711÷(711)

9a10÷15a8

1225

−625÷4

(−1556)÷(−316)

5

−6611

p2q5

5p2q

415−223

924294

13

2d+9d

313+(413)

713

2225+940

25+(75)

−1

310+(58)

34÷x3

94x

2322(34)2

514+18956

3

Evaluate.

x+13 when

  1. x=23
  2. x=56

In the following exercises, solve the equation.

y+35=75

y=45

a310=910

f+(23)=512

f=1312

m−2=−16

23c=18

c = −27

Translate and solve: The quotient of p and −4 is −8. Solve for p.