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Mathematics LibreTexts

3.5: Solve Equations Using Integers; The Division Property of Equality (Part 2)

Translate to an Equation and Solve

In the past several examples, we were given an equation containing a variable. In the next few examples, we’ll have to first translate word sentences into equations with variables and then we will solve the equations.

Example 3.66:

Translate and solve: five more than x is equal to −3.

Solution
Translate. x + 5 = −3
Subtract 5 from both sides. x + 5 − 5 = −3 − 5
Simplify. x = −8

Check the answer by substituting it into the original equation.

$$\begin{split} x + 5 & = -3 \\ -8 + 5 & \stackrel{?}{=} -3 \\ -3 & = -3 \; \checkmark \end{split}$$

Exercise 3.131:

Translate and solve: Seven more than x is equal to −2.

Exercise 3.132:

Translate and solve: Eleven more than y is equal to 2.

Example 3.67:

Translate and solve: the difference of n and 6 is −10.

Solution
Translate. n − 6 = −10
Add 6 to each side. n − 6 + 6 = −10 + 6
Simplify. n = −4

Check the answer by substituting it into the original equation.

$$\begin{split} n - 6 & = -10 \\ -4 - 6 & \stackrel{?}{=} -10 \\ -10 & = -10 \; \checkmark \end{split}$$

Exercise 3.133:

Translate and solve: The difference of p and 2 is −4.

Exercise 3.134:

Translate and solve: The difference of q and 7 is −3.

Example 3.68:

Translate and solve: the number 108 is the product of −9 and y.

Solution
Translate. 108 = −9y
Divide by −9. $$\frac{108}{-9} = \frac{-9y}{-9}$$
Simplify. −12 = y

Check the answer by substituting it into the original equation.

$$\begin{split} 108 & = -9y \\ 108 & \stackrel{?}{=}-9(-12) \\ 108 & = 108 \; \checkmark \end{split}$$

Exercise 3.135:

Translate and solve: The number 132 is the product of −12 and y.

Exercise 3.136:

Translate and solve: The number 117 is the product of −13 and z.

Practice Makes Perfect

Determine Whether a Number is a Solution of an Equation

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

  1. 4x − 2 = 6
    1. x = −2
    2. x = −1
    3. x = 2
  2. 4y − 10 = −14
    1. y = −6
    2. y = −1
    3. y = 1
  3. 9a + 27 = −63
    1. a = 6
    2. a = −6
    3. a = −10
  4. 7c + 42 = −56
    1. c = 2
    2. c = −2
    3. c = −14

Solve Equations Using the Addition and Subtraction Properties of Equality

In the following exercises, solve for the unknown.

  1. n + 12 = 5
  2. m + 16 = 2
  3. p + 9 = −8
  4. q + 5 = −6
  5. u − 3 = −7
  6. v − 7 = −8
  7. h − 10 = −4
  8. k − 9 = −5
  9. x + (−2) = −18
  10. y + (−3) = −10
  11. r − (−5) = −9
  12. s − (−2) = −11

Model the Division Property of Equality

In the following exercises, write the equation modeled by the envelopes and counters and then solve it.

Solve Equations Using the Division Property of Equality

In the following exercises, solve each equation using the division property of equality and check the solution.

  1. 5x = 45
  2. 4p = 64
  3. −7c = 56
  4. −9x = 54
  5. −14p = −42
  6. −8m = −40
  7. −120 = 10q
  8. −75 = 15y
  9. 24x = 480
  10. 18n = 540
  11. −3z = 0
  12. 4u = 0

Translate to an Equation and Solve

In the following exercises, translate and solve.

  1. Four more than n is equal to 1.
  2. Nine more than m is equal to 5.
  3. The sum of eight and p is −3.
  4.  The sum of two and q is −7.
  5. The difference of a and three is −14.
  6. The difference of b and 5 is −2.
  7. The number −42 is the product of −7 and x.
  8. The number −54 is the product of −9 and y.
  9. The product of f and −15 is 75.
  10. The product of g and −18 is 36.
  11. −6 plus c is equal to 4.
  12. −2 plus d is equal to 1.
  13. Nine less than n is −4.
  14. Thirteen less than n is −10 .

Mixed Practice

In the following exercises, solve.

  1. (a) x + 2 = 10 (b) 2x = 10
  2. (a) y + 6 = 12 (b) 6y = 12
  3. (a) −3p = 27 (b) p − 3 = 27
  4. (a) −2q = 34 (b) q − 2 = 34
  5. a − 4 = 16
  6. b − 1 = 11
  7. −8m = −56
  8. −6n = −48
  9. −39 = u + 13
  10. −100 = v + 25
  11. 11r = −99
  12. 15s = −300
  13. 100 = 20d
  14. 250 = 25n
  15. −49 = x − 7
  16. 64 = y − 4

Everyday Math

  1. Cookie packaging A package of 51 cookies has 3 equal rows of cookies. Find the number of cookies in each row, c, by solving the equation 3c = 51.
  2. Kindergarten class Connie’s kindergarten class has 24 children. She wants them to get into 4 equal groups. Find the number of children in each group, g, by solving the equation 4g = 24.

Writing Exercises

  1. Is modeling the Division Property of Equality with envelopes and counters helpful to understanding how to solve the equation 3x = 15? Explain why or why not.
  2. Suppose you are using envelopes and counters to model solving the equations x + 4 = 12 and 4x = 12. Explain how you would solve each equation.
  3. Frida started to solve the equation −3x = 36 by adding 3 to both sides. Explain why Frida’s method will not solve the equation.
  4. Raoul started to solve the equation 4y = 40 by subtracting 4 from both sides. Explain why Raoul’s method will not solve the equation.

Self Check

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

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

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