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 #83 : Equations / Inequalities

Solve for \(\displaystyle x\):

\(\displaystyle 3x-1>x+7\)

Possible Answers:

\(\displaystyle x>2\)

\(\displaystyle x< 4\)

None of the other answers

\(\displaystyle x< 2\)

\(\displaystyle x>4\)

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:

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

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

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

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

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

Give the solution set of the inequality:

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

Possible Answers:

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

\(\displaystyle (-16,16)\)

The set of all real numbers

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

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

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 #4 : How To Find The Solution To An Inequality With Division

Give the solution set of the inequality:

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

Possible Answers:

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

\(\displaystyle (-13,13)\)

The inequality has no solution.

\(\displaystyle [-13,\infty)\)

\(\displaystyle (-\infty , -13]\)

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

Give the solution set of the inequality:

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

Possible Answers:

\(\displaystyle [-7,\infty )\)

\(\displaystyle [-7,7]\)

\(\displaystyle [7,\infty )\)

The inequality has no solution.

\(\displaystyle (-\infty , -7]\)

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 #91 : Equations / Inequalities

Give the solution set of the inequality:

\(\displaystyle -4x - 11 < 57\)

Possible Answers:

\(\displaystyle (-\infty,-17 )\)

\(\displaystyle (-17,\infty )\)

The set of all real numbers

\(\displaystyle (-17,17)\)

\(\displaystyle (17,\infty )\)

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 #92 : Equations / Inequalities

Give the solution set of the inequality:

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

Possible Answers:

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

\(\displaystyle (-14,14)\)

The set of all real numbers

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

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

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 #93 : Equations / Inequalities

Solve for \(\displaystyle x\):

\(\displaystyle 2-6x>10-2x\)

Possible Answers:

\(\displaystyle x>2\)

\(\displaystyle x< -2\)

None of the other answers

\(\displaystyle x< 2\)

\(\displaystyle x>-2\)

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 #1 : 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:

\(\displaystyle (14,19)\)

\(\displaystyle (-\infty , \infty )\)

\(\displaystyle (14, \infty )\)

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

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

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 #95 : Equations / Inequalities

Solve for \(\displaystyle x\):

\(\displaystyle 0.4 x - 1.7 \geq -8.5\)

Possible Answers:

\(\displaystyle [1.7, \infty )\)

\(\displaystyle [-1.7, \infty )\)

\(\displaystyle [17, \infty )\)

\(\displaystyle [-17, \infty )\)

The inequality has no solution.

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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