Algebra 1 : How to find the solution to an inequality with division

Study concepts, example questions & explanations for Algebra 1

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Example Questions

Example Question #86 : Systems Of Inequalities

Solve for \displaystyle x:

\displaystyle 3x-1>x+7

Possible Answers:

\displaystyle x>2

None of the other answers

\displaystyle x< 2

\displaystyle x< 4

\displaystyle x>4

Correct answer:

\displaystyle x>4

Explanation:

To solve for \displaystyle x, separate the integers and \displaystyle x's by adding 1 and subtracting \displaystyle x from both sides to get \displaystyle 2x>8. Then, divide both sides by 2 to get \displaystyle x>4. Since you didn't divide by a negative number, the sign does not need to be reversed.

Example Question #2 : How To Find The Solution To An Inequality With Division

Solve the following:   \displaystyle -2x+3>4

Possible Answers:

\displaystyle x< -\frac{7}{2}

\displaystyle x>-\frac{7}{2}

\displaystyle x< -\frac{1}{2}

\displaystyle x>-\frac{1}{2}

Correct answer:

\displaystyle x< -\frac{1}{2}

Explanation:

\displaystyle -2x+3-3>4-3

\displaystyle -2x>1

\displaystyle \frac{-2x}{-2}< \frac{1}{-2}    Don't forget to change the direction of the inequality sign when dividing by a negative number!

\displaystyle x< -\frac{1}{2}

Example Question #87 : Systems Of Inequalities

Give the solution set of the inequality:

\displaystyle -4x + 17 > 81

Possible Answers:

\displaystyle (-\infty ,-16)

\displaystyle \left (-16, \infty \right )

\displaystyle (-\infty ,16)

The set of all real numbers

\displaystyle (-16,16)

Correct answer:

\displaystyle (-\infty ,-16)

Explanation:

\displaystyle -4x + 17 > 81

\displaystyle -4x + 17 -17 > 81 -17

\displaystyle -4x > 64

\displaystyle -4x \div (-4)< 64 \div (-4)

Note change in direction of the inequality symbol when the expressions are divided by a negative number.

\displaystyle x < -16

or, in interval form,

\displaystyle (-\infty ,-16)

 

Example Question #3 : How To Find The Solution To An Inequality With Division

Give the solution set of the inequality:

\displaystyle -5x + 17 \geq 82

Possible Answers:

\displaystyle \left [13, \infty \right )

\displaystyle [-13,\infty)

\displaystyle (-13,13)

\displaystyle (-\infty , -13]

The inequality has no solution.

Correct answer:

\displaystyle (-\infty , -13]

Explanation:

\displaystyle -5x + 17 \geq 82

\displaystyle -5x + 17 -17 \geq 82-17

\displaystyle -5x \geq 65

\displaystyle -5x \div (-5) \leq 65\div (-5) 

Note change in direction of the inequality symbol when the expressions are divided by a negative number.

\displaystyle x \leq -13 

or, in interval form,

\displaystyle (-\infty , -13]

Example Question #1 : How To Find The Solution To An Inequality With Division

Give the solution set of the inequality:

\displaystyle -5x + 27 \leq 62

Possible Answers:

\displaystyle [-7,7]

\displaystyle [-7,\infty )

The inequality has no solution.

\displaystyle (-\infty , -7]

\displaystyle [7,\infty )

Correct answer:

\displaystyle [-7,\infty )

Explanation:

\displaystyle -5x + 27 \leq 62

\displaystyle -5x + 27 -27 \leq 62-27

\displaystyle -5x \leq 35

\displaystyle -5x \div (-5) \leq 35\div (-5) 

Note change in direction of the inequality symbol when the expressions are divided by a negative number.

\displaystyle x \geq -7 

or, in interval form,

\displaystyle [-7,\infty )

Example Question #1 : How To Find The Solution To An Inequality With Division

Give the solution set of the inequality:

\displaystyle -4x - 11 < 57

Possible Answers:

\displaystyle (-17,\infty )

\displaystyle (-\infty,-17 )

\displaystyle (-17,17)

\displaystyle (17,\infty )

The set of all real numbers

Correct answer:

\displaystyle (-17,\infty )

Explanation:

\displaystyle -4x - 11 < 57

\displaystyle -4x - 11 + 11 < 57 + 11

\displaystyle -4x < 68

\displaystyle -4x \div (-4) > 68 \div (-4)

Note change in direction of the inequality symbol when the expressions are divided by a negative number.

\displaystyle x > -17

or, in interval form,

\displaystyle (-17,\infty )

Example Question #5 : How To Find The Solution To An Inequality With Division

Give the solution set of the inequality:

\displaystyle -4x + 11 < 67

Possible Answers:

\displaystyle (-14,14)

\displaystyle (-\infty ,-14 )

The set of all real numbers

\displaystyle (-\infty ,14 )

\displaystyle (-14, \infty )

Correct answer:

\displaystyle (-14, \infty )

Explanation:

\displaystyle -4x + 11 < 67

\displaystyle -4x + 11 - 11 < 67- 11

\displaystyle -4x < 56

\displaystyle -4x \div (-4) > 56 \div (-4)

Note change in direction of the inequality symbol when the expressions are divided by a negative number.

\displaystyle x > -14

or, in interval form,

\displaystyle (-14, \infty )

Example Question #1 : How To Find The Solution To An Inequality With Division

Solve for \displaystyle x:

\displaystyle 2-6x>10-2x

Possible Answers:

\displaystyle x< -2

\displaystyle x< 2

\displaystyle x>2

\displaystyle x>-2

None of the other answers

Correct answer:

\displaystyle x< -2

Explanation:

First, add \displaystyle 2x and subtract \displaystyle 2 from both sides of the inequality to get \displaystyle -4x>8.

Then, divide both sides by \displaystyle -4 and reverse the sign since you are dividing by a negative number.

This gives you \displaystyle x< -2.

Example Question #2 : How To Find The Solution To An Inequality With Division

Find the solution set to the following compound inequality statement:

\displaystyle 4y + 15 < 91 \textrm{ and } 7y -12 > 86

Possible Answers:

\displaystyle (14, \infty )

\displaystyle (-\infty , 19)

\displaystyle (14,19)

\displaystyle (-\infty , \infty )

\displaystyle (-\infty , 14) \cup (19, \infty )

Correct answer:

\displaystyle (14,19)

Explanation:

Solve each of these two inequalities separately:

 

\displaystyle 4y + 15 < 91

\displaystyle 4y + 15 - 15 < 91- 15

\displaystyle 4y < 76

\displaystyle 4y \div 4 < 76 \div 4

\displaystyle y < 19, or, in interval form, \displaystyle (-\infty , 19)

 

\displaystyle 7y -12 > 86

\displaystyle 7y -12 + 12 > 86 + 12

\displaystyle 7y > 98

\displaystyle 7y \div 7 > 98 \div 7

\displaystyle y > 14, or, in interval form, \displaystyle (14, \infty )

 

The two inequalities are connected with an "and", so we take the intersection of the two intervals.

\displaystyle (14, \infty ) \cap (-\infty , 19) = (14,19)

Example Question #3 : How To Find The Solution To An Inequality With Division

Solve for \displaystyle x:

\displaystyle 0.4 x - 1.7 \geq -8.5

Possible Answers:

\displaystyle [-1.7, \infty )

\displaystyle [-17, \infty )

The inequality has no solution.

\displaystyle [1.7, \infty )

\displaystyle [17, \infty )

Correct answer:

\displaystyle [-17, \infty )

Explanation:

\displaystyle 0.4 x - 1.7 \geq -8.5

\displaystyle 0.4 x - 1.7 + 1.7 \geq -8.5+ 1.7

\displaystyle 0.4 x \geq -6.8

\displaystyle 0.4 x \div 0.4 \geq -6.8\div 0.4

\displaystyle x \geq -17

or, in interval form, \displaystyle [-17, \infty )

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