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

Study concepts, example questions & explanations for Algebra 1

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Example Questions

Example Question #21 : Equations / Inequalities

Solve:  \displaystyle \frac{4}{7}x > 7

Possible Answers:

\displaystyle x>\frac{1}{4}

\displaystyle x< \frac{49}{4}

\displaystyle x< \frac{45}{4}

\displaystyle x>\frac{49}{4}

\displaystyle x>4

Correct answer:

\displaystyle x>\frac{49}{4}

Explanation:

To isolate the x variable, multiply the reciprocal of the fraction in front of the variable on both sides of the inequality.

\displaystyle \frac{4}{7}x \cdot \frac{7}{4}> 7\cdot \frac{7}{4}

Simplify both sides of the inequality.

The answer is:  \displaystyle x>\frac{49}{4}

Example Question #21 : Systems Of Inequalities

Solve the following inequality:  \displaystyle \frac{1}{3}x + \frac{2}{3}>3

Possible Answers:

\displaystyle x>7

\displaystyle x>-\frac{7}{3}

\displaystyle x>1

\displaystyle x< 7

\displaystyle x>\frac{7}{3}

Correct answer:

\displaystyle x>7

Explanation:

In order to eliminate the fractions, multiply the inequality by three on both sides.

This will make the inequality easier to solve.

\displaystyle 3(\frac{1}{3}x + \frac{2}{3})>3(3)

Distribute and simplify both sides.

\displaystyle x+2>9

Subtract two from both sides.

\displaystyle x+2-2>9-2

The answer is:  \displaystyle x>7

Example Question #23 : Equations / Inequalities

Solve the inequality:  \displaystyle \frac{2}{3}x >15

Possible Answers:

\displaystyle x>\frac{13}{3}

\displaystyle x< \frac{45}{2}

\displaystyle x>\frac{45}{2}

\displaystyle x>\frac{43}{3}

\displaystyle x< \frac{43}{3}

Correct answer:

\displaystyle x>\frac{45}{2}

Explanation:

Multiply both sides by three halves.

\displaystyle \frac{2}{3}x \cdot \frac{3}{2} >15 \cdot \frac{3}{2}

Simplify both sides.  Multiply the integer with the numerator on the right side of the inequality.

The answer is:  \displaystyle x>\frac{45}{2}

Example Question #22 : Systems Of Inequalities

Solve the following inequality:  \displaystyle \frac{2}{7}x < 7

Possible Answers:

\displaystyle x< \frac{49}{2}

\displaystyle x>\frac{49}{2}

\displaystyle x\leq\frac{47}{7}

\displaystyle x\leq\frac{49}{2}

\displaystyle x< \frac{47}{7}

Correct answer:

\displaystyle x< \frac{49}{2}

Explanation:

Solve this inequality by multiplying both sides by the reciprocal of the coefficient in front of the x-variable.

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

Simplify both sides.  Multiply the integer by the numerator on the right side of the inequality.

The answer is:  \displaystyle x< \frac{49}{2}

Example Question #21 : Equations / Inequalities

Solve the following inequality:  \displaystyle \frac{2}{5}x>40

Possible Answers:

\displaystyle x>100

\displaystyle x>\frac{35}{2}

\displaystyle x>10

\displaystyle x>4

\displaystyle x>16

Correct answer:

\displaystyle x>100

Explanation:

Multiply the reciprocal of the fraction in front of the \displaystyle x variable on both sides of the equation.

\displaystyle \frac{2}{5}x \cdot \frac{5}{2}>40\cdot \frac{5}{2}

Simplify both sides.

\displaystyle x>\frac{200}{2}

Reduce the fraction on the right side.

The answer is:  \displaystyle x>100

Example Question #21 : Systems Of Inequalities

Solve the inequality:  \displaystyle \frac{3}{4}x>-4

Possible Answers:

\displaystyle x< -\frac{16}{3}

\displaystyle x>-2

\displaystyle x>-\frac{1}{3}

\displaystyle x>-4

\displaystyle x>-\frac{16}{3}

Correct answer:

\displaystyle x>-\frac{16}{3}

Explanation:

Multiply both sides by the reciprocal of the fraction in front of the x-variable.

\displaystyle \frac{3}{4}x\cdot \frac{4}{3}>-4\cdot \frac{4}{3}

Simplify both sides.  There is no need to switch the sign.  Multiply the negative integer with the numerator on the right side of the inequality.

The answer is:  \displaystyle x>-\frac{16}{3}

Example Question #21 : Systems Of Inequalities

Solve the inequality:  \displaystyle 9x\leq -\frac{1}{3}

Possible Answers:

\displaystyle x< -\frac{1}{27}

\displaystyle x\leq -\frac{1}{27}

\displaystyle x\leq -\frac{1}{3}

\displaystyle x\geq -\frac{1}{27}

\displaystyle x\geq -\frac{1}{3}

Correct answer:

\displaystyle x\leq -\frac{1}{27}

Explanation:

In order to isolate the x-variable, we will need to divide both sides by nine.  To avoid writing a complex fraction on the right side, dividing by nine is similar to multiplying by one-ninth.

Multiply by one-ninth on both sides.

\displaystyle 9x \cdot \frac{1}{9}\leq -\frac{1}{3} \cdot \frac{1}{9}

Simplify both sides.  Multiply the denominator with denominator on the right side.  Since we have divide by a positive number on both sides, there is no need to switch the sign.

The answer is:  \displaystyle x\leq -\frac{1}{27}

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