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Prealgebra

5.4 Solve Equations with Decimals

Prealgebra5.4 Solve Equations with Decimals

Learning Objectives

By the end of this section, you will be able to:
  • Determine whether a decimal is a solution of an equation
  • Solve equations with decimals
  • Translate to an equation and solve

Be Prepared 5.4

Before you get started, take this readiness quiz.

  1. Evaluate x+23whenx=−14.x+23whenx=−14.
     If you missed this problem, review Example 4.77.
  2. Evaluate 15−y15−y when y=−5.y=−5.
     If you missed this problem, review Example 3.41.
  3. Solve n−7=42.n−7=42.
     If you missed this problem, review Example 4.99.

Determine Whether a Decimal is a Solution of an Equation

Solving equations with decimals is important in our everyday lives because money is usually written with decimals. When applications involve money, such as shopping for yourself, making your family’s budget, or planning for the future of your business, you’ll be solving equations with decimals.

Now that we’ve worked with decimals, we are ready to find solutions to equations involving decimals. 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, a fraction, or a decimal. We’ll list these steps here again for easy reference.

How To

Determine whether a number is a solution to an equation.

  1. Step 1. Substitute the number for the variable in the equation.
  2. Step 2. Simplify the expressions on both sides of the equation.
  3. Step 3.
    Determine whether the resulting equation is true.
    • If so, the number is a solution.
    • If not, the number is not a solution.

Example 5.40

Determine whether each of the following is a solution of x−0.7=1.5:x−0.7=1.5:

ⓐx=1x=1ⓑx=−0.8x=−0.8ⓒx=2.2x=2.2

Try It 5.79

Determine whether each value is a solution of the given equation.

x−0.6=1.3:x−0.6=1.3:ⓐx=0.7x=0.7ⓑx=1.9x=1.9ⓒx=−0.7x=−0.7

Try It 5.80

Determine whether each value is a solution of the given equation.

y−0.4=1.7:y−0.4=1.7:ⓐy=2.1y=2.1ⓑy=1.3y=1.3ⓒ−1.3−1.3

Solve Equations with Decimals

In previous chapters, we solved equations using the Properties of Equality. We will use these same properties to solve equations with decimals.

Properties of Equality

Subtraction Property of Equality
For any numbers a,b,andc,a,b,andc,
If a=b,a=b, then a−c=b−c.a−c=b−c.		 Addition Property of Equality
 For any numbers a,b,andc,a,b,andc,
If a=b,a=b, then a+c=b+c.a+c=b+c.
The Division Property of Equality
 For any numbers a,b,andc,andc≠0a,b,andc,andc≠0
If a=b,a=b, then ac=bcac=bc		 The Multiplication Property of Equality
 For any numbers a,b,andc,a,b,andc,
If a=b,a=b, then ac=bcac=bc

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

Example 5.41

Solve: y+2.3=−4.7.y+2.3=−4.7.

Try It 5.81

Solve: y+2.7=−5.3.y+2.7=−5.3.

Try It 5.82

Solve: y+3.6=−4.8.y+3.6=−4.8.

Example 5.42

Solve: a−4.75=−1.39.a−4.75=−1.39.

Try It 5.83

Solve: a−3.93=−2.86.a−3.93=−2.86.

Try It 5.84

Solve: n−3.47=−2.64.n−3.47=−2.64.

Example 5.43

Solve: −4.8=0.8n.−4.8=0.8n.

Try It 5.85

Solve: −8.4=0.7b.−8.4=0.7b.

Try It 5.86

Solve: −5.6=0.7c.−5.6=0.7c.

Example 5.44

Solve: p−1.8=−6.5.p−1.8=−6.5.

Try It 5.87

Solve: c−2.6=−4.5.c−2.6=−4.5.

Try It 5.88

Solve: b−1.2=−5.4.b−1.2=−5.4.

Translate to an Equation and Solve

Now that we have solved equations with decimals, we are ready to translate word sentences to equations and solve. Remember to look for words and phrases that indicate the operations to use.

Example 5.45

Translate and solve: The difference of nn and 4.34.3 is 2.1.2.1.

Try It 5.89

Translate and solve: The difference of yy and 4.94.9 is 2.8.2.8.

Try It 5.90

Translate and solve: The difference of zz and 5.75.7 is 3.4.3.4.

Example 5.46

Translate and solve: The product of −3.1−3.1 and xx is 5.27.5.27.

Try It 5.91

Translate and solve: The product of −4.3−4.3 and xx is 12.04.12.04.

Try It 5.92

Translate and solve: The product of −3.1−3.1 and mm is 26.66.26.66.

Example 5.47

Translate and solve: The quotient of pp and −2.4−2.4 is 6.5.6.5.

Try It 5.93

Translate and solve: The quotient of qq and −3.4−3.4 is 4.5.4.5.

Try It 5.94

Translate and solve: The quotient of rr and −2.6−2.6 is 2.5.2.5.

Example 5.48

Translate and solve: The sum of nn and 2.92.9 is 1.7.1.7.

Try It 5.95

Translate and solve: The sum of jj and 3.83.8 is 2.6.2.6.

Try It 5.96

Translate and solve: The sum of kk and 4.74.7 is 0.3.0.3.

Section 5.4 Exercises

Practice Makes Perfect

Determine Whether a Decimal is a Solution of an Equation

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

285.

x − 0.8 = 2.3 x − 0.8 = 2.3
ⓐ x = 2 x = 2 ⓑ x = −1.5 x = −1.5 ⓒ x = 3.1 x = 3.1

286.

y+0.6=−3.4y+0.6=−3.4
 ⓐy=−4y=−4ⓑy=−2.8y=−2.8ⓒy=2.6y=2.6

287.

h1.5=−4.3h1.5=−4.3
 ⓐh=6.45h=6.45ⓑh=−6.45h=−6.45ⓒh=−2.1h=−2.1

288.

0.75k=−3.60.75k=−3.6
 ⓐk=−0.48k=−0.48ⓑk=−4.8k=−4.8ⓒk=−2.7k=−2.7

Solve Equations with Decimals

In the following exercises, solve the equation.

289.

y + 2.9 = 5.7 y + 2.9 = 5.7

290.

m + 4.6 = 6.5 m + 4.6 = 6.5

291.

f + 3.45 = 2.6 f + 3.45 = 2.6

292.

h + 4.37 = 3.5 h + 4.37 = 3.5

293.

a + 6.2 = −1.7 a + 6.2 = −1.7

294.

b + 5.8 = −2.3 b + 5.8 = −2.3

295.

c + 1.15 = −3.5 c + 1.15 = −3.5

296.

d + 2.35 = −4.8 d + 2.35 = −4.8

297.

n − 2.6 = 1.8 n − 2.6 = 1.8

298.

p − 3.6 = 1.7 p − 3.6 = 1.7

299.

x − 0.4 = −3.9 x − 0.4 = −3.9

300.

y − 0.6 = −4.5 y − 0.6 = −4.5

301.

j − 1.82 = −6.5 j − 1.82 = −6.5

302.

k − 3.19 = −4.6 k − 3.19 = −4.6

303.

m − 0.25 = −1.67 m − 0.25 = −1.67

304.

q − 0.47 = −1.53 q − 0.47 = −1.53

305.

0.5 x = 3.5 0.5 x = 3.5

306.

0.4 p = 9.2 0.4 p = 9.2

307.

−1.7 c = 8.5 −1.7 c = 8.5

308.

−2.9 x = 5.8 −2.9 x = 5.8

309.

−1.4 p = −4.2 −1.4 p = −4.2

310.

−2.8 m = −8.4 −2.8 m = −8.4

311.

−120 = 1.5 q −120 = 1.5 q

312.

−75 = 1.5 y −75 = 1.5 y

313.

0.24 x = 4.8 0.24 x = 4.8

314.

0.18 n = 5.4 0.18 n = 5.4

315.

−3.4 z = −9.18 −3.4 z = −9.18

316.

−2.7 u = −9.72 −2.7 u = −9.72

317.

a 0.4 = −20 a 0.4 = −20

318.

b 0.3 = −9 b 0.3 = −9

319.

x 0.7 = −0.4 x 0.7 = −0.4

320.

y 0.8 = −0.7 y 0.8 = −0.7

321.

p − 5 = −1.65 p − 5 = −1.65

322.

q − 4 = −5.92 q − 4 = −5.92

323.

r − 1.2 = −6 r − 1.2 = −6

324.

s − 1.5 = −3 s − 1.5 = −3

Mixed Practice

In the following exercises, solve the equation. Then check your solution.

325.

x − 5 = −11 x − 5 = −11

326.

− 2 5 = x + 3 4 − 2 5 = x + 3 4

327.

p + 8 = −2 p + 8 = −2

328.

p + 2 3 = 1 12 p + 2 3 = 1 12

329.

−4.2 m = −33.6 −4.2 m = −33.6

330.

q + 9.5 = −14 q + 9.5 = −14

331.

q + 5 6 = 1 12 q + 5 6 = 1 12

332.

8.6 15 = − d 8.6 15 = − d

333.

7 8 m = 1 10 7 8 m = 1 10

334.

j − 6.2 = −3 j − 6.2 = −3

335.

− 2 3 = y + 3 8 − 2 3 = y + 3 8

336.

s − 1.75 = −3.2 s − 1.75 = −3.2

337.

11 20 = − f 11 20 = − f

338.

−3.6 b = 2.52 −3.6 b = 2.52

339.

−4.2 a = 3.36 −4.2 a = 3.36

340.

−9.1 n = −63.7 −9.1 n = −63.7

341.

r − 1.25 = −2.7 r − 1.25 = −2.7

342.

1 4 n = 7 10 1 4 n = 7 10

343.

h − 3 = −8 h − 3 = −8

344.

y − 7.82 = −16 y − 7.82 = −16

Translate to an Equation and Solve

In the following exercises, translate and solve.

345.

The difference of nn and 1.91.9 is 3.4.3.4.

346.

The difference nn and 1.51.5 is 0.8.0.8.

347.

The product of −6.2−6.2 and xx is −4.96.−4.96.

348.

The product of −4.6−4.6 and xx is −3.22.−3.22.

349.

The quotient of yy and −1.7−1.7 is −5.−5.

350.

The quotient of zz and −3.6−3.6 is 3.3.

351.

The sum of nn and −7.3−7.3 is 2.4.2.4.

352.

The sum of nn and −5.1−5.1 is 3.8.3.8.

Everyday Math

353.

Shawn bought a pair of shoes on sale for $78$78. Solve the equation 0.75p=780.75p=78 to find the original price of the shoes, p.p.

354.

Mary bought a new refrigerator. The total price including sales tax was $1,350.$1,350. Find the retail price, r,r, of the refrigerator before tax by solving the equation 1.08r=1,350.1.08r=1,350.

Writing Exercises

355.

Think about solving the equation 1.2y=60,1.2y=60, but do not actually solve it. Do you think the solution should be greater than 6060 or less than 60?60? Explain your reasoning. Then solve the equation to see if your thinking was correct.

356.

Think about solving the equation 0.8x=200,0.8x=200, but do not actually solve it. Do you think the solution should be greater than 200200 or less than 200?200? Explain your reasoning. Then solve the equation to see if your thinking was correct.

Self Check

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

.

ⓑ On a scale of 1–10, how would you rate your mastery of this section in light of your responses on the checklist? How can you improve this?

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