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8.4 Solve Equations with Fraction or Decimal Coefficients

Solve Equations with Fraction Coefficients

Let’s use the General Strategy for Solving Linear Equations introduced earlier to solve the equation 18x+12=14.

A mathematical equation is displayed: 1/8x + 1/2 = 1/4. This is a linear equation with one variable, x, involving fractions.
To isolate the x term, subtract 12 from both sides.
An algebraic equation: 1/8x + 1/2 - 1/2 = 1/4 - 1/2, with the -1/2 terms highlighted in red, likely for simplification.
Simplify the left side.
A mathematical equation is displayed, showing '1/8x = 1/4 - 1/2' in black text against a white background.
Change the constants to equivalent fractions with the LCD.
A mathematical equation is displayed: 1/8x = 1/4 - 2/4. The equation involves fractions and a variable 'x'.
Subtract.
The image displays the algebraic equation '1/8x = -1/4' centered on a white background.
Multiply both sides by the reciprocal of 18.
The equation (8/1)*(1/8)x = (8/1)(-1/4) illustrates multiplying both sides by 8/1 (highlighted in red) to solve for the variable x.
Simplify.
The equation x = -2 is displayed, representing a vertical line on a coordinate plane or a simple algebraic solution for x.

This method worked fine, but many students don’t feel very confident when they see all those fractions. So we are going to show an alternate method to solve equations with fractions. This alternate method eliminates the fractions.

We will apply the Multiplication Property of Equality and multiply both sides of an equation by the least common denominator of all the fractions in the equation. The result of this operation will be a new equation, equivalent to the first, but with no fractions. This process is called clearing the equation of fractions. Let’s solve the same equation again, but this time use the method that clears the fractions.

Notice in Example 1 that once we cleared the equation of fractions, the equation was like those we solved earlier in this chapter. We changed the problem to one we already knew how to solve! We then used the General Strategy for Solving Linear Equations.

In the next example, we’ll have variables and fractions on both sides of the equation.

In Example 4, we’ll start by using the Distributive Property. This step will clear the fractions right away!

Many times, there will still be fractions, even after distributing.

Solve Equations with Decimal Coefficients

Some equations have decimals in them. This kind of equation will occur when we solve problems dealing with money and percent. But decimals are really another way to represent fractions. For example, 0.3=310 and 0.17=17100. So, when we have an equation with decimals, we can use the same process we used to clear fractions—multiply both sides of the equation by the least common denominator.

The next example uses an equation that is typical of the ones we will see in the money applications in the next chapter. Notice that we will distribute the decimal first before we clear all decimals in the equation.

Key Concepts

  • Solve equations with fraction coefficients by clearing the fractions.
    1. Find the least common denominator of all the fractions in the equation.
    2. Multiply both sides of the equation by that LCD. This clears the fractions.
    3. Solve using the General Strategy for Solving Linear Equations.

Section Exercises

Practice Makes Perfect

Solve equations with fraction coefficients

In the following exercises, solve the equation by clearing the fractions.

14x12=34

x = −1

34x12=14

56y23=32

y = −1

56y13=76

12a+38=34

a=34

58b+12=34

2=13x12x+23x

x = 4

2=35x13x+25x

14m45m+12m=−1

m = 20

56n14n12n=−2

x+12=23x12

x = −3

x+34=12x54

13w+54=w14

w=94

32z+13=z23

12x14=112x+16

x = 1

12a14=16a+112

13b+15=25b35

b = 12

13x+25=15x25

1=16(12x6)

x = 1

1=15(15x10)

14(p7)=13(p+5)

p = −41

15(q+3)=12(q3)

12(x+4)=34

x=52

13(x+5)=56

Solve Equations with Decimal Coefficients

In the following exercises, solve the equation by clearing the decimals.

0.6y+3=9

y = 10

0.4y4=2

3.6j2=5.2

j = 2

2.1k+3=7.2

0.4x+0.6=0.5x1.2

x = 18

0.7x+0.4=0.6x+2.4

0.23x+1.47=0.37x1.05

x = 18

0.48x+1.56=0.58x0.64

0.9x1.25=0.75x+1.75

x = 20

1.2x0.91=0.8x+2.29

0.05n+0.10(n+8)=2.15

n = 9

0.05n+0.10(n+7)=3.55

0.10d+0.25(d+5)=4.05

d = 8

0.10d+0.25(d+7)=5.25

0.05(q5)+0.25q=3.05

q = 11

0.05(q8)+0.25q=4.10

Everyday Math

Coins Taylor has $2.00 in dimes and pennies. The number of pennies is 2 more than the number of dimes. Solve the equation 0.10d+0.01(d+2)=2 for d, the number of dimes.

d = 18

Stamps Travis bought $9.45 worth of 49-cent stamps and 21-cent stamps. The number of 21-cent stamps was 5 less than the number of 49-cent stamps. Solve the equation 0.49s+0.21(s5)=9.45 for s, to find the number of 49-cent stamps Travis bought.

Writing Exercises

Explain how to find the least common denominator of 38,16,and23.

Answers will vary.

If an equation has several fractions, how does multiplying both sides by the LCD make it easier to solve?

If an equation has fractions only on one side, why do you have to multiply both sides of the equation by the LCD?

Answers will vary.

In the equation 0.35x+2.1=3.85, what is the LCD? How do you know?

Self Check

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

A self-assessment chart for math skills, asking students to rate their ability to solve equations using a general strategy, with fraction coefficients, and with decimal coefficients, across three confidence levels.
Figure 8.7

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

Chapter Review Exercises

Solve Equations using the Subtraction and Addition Properties of Equality

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

x+16=31,x=15

yes

w8=5,w=3

−9n=45,n=54

no

4a=72,a=18

In the following exercises, solve the equation using the Subtraction Property of Equality.

x+7=19

12

y+2=−6

a+13=53

a=43

n+3.6=5.1

In the following exercises, solve the equation using the Addition Property of Equality.

u7=10

u = 17

x9=−4

c311=911

c=1211

p4.8=14

In the following exercises, solve the equation.

n12=32

n = 44

y+16=−9

f+23=4

f=103

d3.9=8.2

y+815=−3

y = 4

7x+106x+3=5

6(n1)5n=−14

n = −8

8(3p+5)23(p1)=35

In the following exercises, translate each English sentence into an algebraic equation and then solve it.

The sum of −6 and m is 25.

−6 + m = 25; m = 31

Four less than n is 13.

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

Rochelle’s daughter is 11 years old. Her son is 3 years younger. How old is her son?

s = 11 − 3; 8 years old

Tan weighs 146 pounds. Minh weighs 15 pounds more than Tan. How much does Minh weigh?

Peter paid $9.75 to go to the movies, which was $46.25 less than he paid to go to a concert. How much did he pay for the concert?

c − 46.25 = 9.75; $56.00

Elissa earned $152.84 this week, which was $21.65 more than she earned last week. How much did she earn last week?

Solve Equations using the Division and Multiplication Properties of Equality

In the following exercises, solve each equation using the Division Property of Equality.

8x=72

x = 9

13a=−65

0.25p=5.25

p = 21

y=4

In the following exercises, solve each equation using the Multiplication Property of Equality.

n6=18

n = 108

y−10=30

36=34x

x = 48

58u=1516

In the following exercises, solve each equation.

−18m=−72

m = 4

c9=36

0.45x=6.75

x = 15

1112=23y

5r3r+9r=352

r = 3

24x+8x11x=−7−14

Solve Equations with Variables and Constants on Both Sides

In the following exercises, solve the equations with constants on both sides.

8p+7=47

p = 5

10w5=65

3x+19=−47

x = −22

32=−49n

In the following exercises, solve the equations with variables on both sides.

7y=6y13

y = −13

5a+21=2a

k=−6k35

k = −5

4x38=3x

In the following exercises, solve the equations with constants and variables on both sides.

12x9=3x+45

x = 6

5n20=−7n80

4u+16=−19u

u = −7

58c4=38c+4

In the following exercises, solve each linear equation using the general strategy.

6(x+6)=24

x = −2

9(2p5)=72

(s+4)=18

s = −22

8+3(n9)=17

233(y7)=8

y = 12

13(6m+21)=m7

8(r2)=6(r+10)

r = 38

5+7(25x)=2(9x+1)(13x57)

4(3.5y+0.25)=365

y = 26

0.25(q8)=0.1(q+7)

Solve Equations with Fraction or Decimal Coefficients

In the following exercises, solve each equation by clearing the fractions.

25n110=710

n = 2

13x+15x=8

34a13=12a+56

a=143

12(k+3)=13(k+16)

In the following exercises, solve each equation by clearing the decimals.

0.8x0.3=0.7x+0.2

x = 5

0.36u+2.55=0.41u+6.8

0.6p1.9=0.78p+1.7

p = −20

0.10d+0.05(d4)=2.05

Chapter Practice Test

Determine whether each number is a solution to the equation.
3x+5=23.

  1. 6
  2. 235
  1. ⓐ yes
  2. ⓑ no

In the following exercises, solve each equation.

n18=31

9c=144

c = 16

4y8=16

−8x15+9x1=−21

x = −5

−15a=120

23x=6

x = 9

x+3.8=8.2

10y=−5y+60

y = 4

8n+2=6n+12

9m24m+m=428

m = 6

−5(2x+1)=45

(d+9)=23

d = −32

13(6m+21)=m7

2(6x+5)8=−22

x = −2

8(3a+5)7(4a3)=203a

14p+13=12

p=23

0.1d+0.25(d+8)=4.1

Translate and solve: The difference of twice x and 4 is 16.

2x − 4 = 16; x = 10

Samuel paid $25.82 for gas this week, which was $3.47 less than he paid last week. How much did he pay last week?