Algebra 1 : Linear Inequalities

Study concepts, example questions & explanations for Algebra 1

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Example Questions

Example Question #1 : Writing Inequalities

Write a compound inequality that describes the given graph:Or_open

Possible Answers:

\displaystyle \small x > 5 \quad or \quad x \le 9

\displaystyle \small x < 5 \quad and \quad x \ge 9

\displaystyle \small x< 5 \quad or \quad x \ge 9

\displaystyle \small x > 5 \quad and \quad x \le 9

\displaystyle \small x \le 5 \quad or \quad x > 9

Correct answer:

\displaystyle \small x< 5 \quad or \quad x \ge 9

Explanation:

The graph shows an arrow beginning on 5 with an open circle and pointing to the left, thus that portion of the graph says, all real numbers less than 5. There is a second arrow beginning on 9 with a closed circle and pointing to the right, representing all real numbers greater than or equal to 9. Since we are joining the two parts of the graph, we have a compound inequality utilizing the "or" statement. So our answer is \displaystyle \small x< 5 \quad or \quad x \ge 9.   

Example Question #1 : Writing Inequalities

Write as an algebraic inequality:

Twenty subtracted from the product of seven and a number exceeds one hundred.

Possible Answers:

\displaystyle 7x - 20 \geq 100

\displaystyle 20-7x > 100

\displaystyle 7(x-20) > 100

\displaystyle 7x - 20 > 100

\displaystyle 20-7x \geq 100

Correct answer:

\displaystyle 7x - 20 > 100

Explanation:

"The product of seven and a number " is \displaystyle 7x. "Twenty subtracted from the product of seven and a number" is \displaystyle 7x - 20 . "Exceeds one hundred" means that this is greater than one hundred, so the correct inequality is

\displaystyle 7x - 20 > 100

Example Question #2 : Writing Inequalities

Write as an algebraic inequality:

Twice the sum of a number and sixteen is no less than sixty.

Possible Answers:

\displaystyle 2 (x+16) \geq 60

\displaystyle 2 (x+16) \neq 60

\displaystyle 2x+16 > 60

\displaystyle 2 (x+16) > 60

\displaystyle 2x+16 \geq 60

Correct answer:

\displaystyle 2 (x+16) \geq 60

Explanation:

"The sum of a number and sixteen" is translates to \displaystyle x + 16; twice that sum is \displaystyle 2(x+16). " Is no less than sixty" means that this is greater than or equal to sixty, so the desired inequality is

 \displaystyle 2(x+16) \geq 60.

Example Question #3 : Writing Inequalities

Write as an algebraic inequality:

Twice the sum of a number and sixteen does not exceed eighty.

Possible Answers:

\displaystyle 2x+16 \leq 80 

\displaystyle 2 (x+16) \leq 80

\displaystyle 2x+16 > 80

\displaystyle 2 (x+16) < 80

\displaystyle 2x+16 \geq 80

Correct answer:

\displaystyle 2 (x+16) \leq 80

Explanation:

"The sum of a number and sixteen" translates to \displaystyle x + 16; twice that sum is \displaystyle 2 (x+16). "Does not exceed eighty" means that it is less than or equal to eighty, so the desired inequality is

\displaystyle 2 (x+16) \leq 80

Example Question #1 : Writing Inequalities

A candy company is inspecting its factory. In a standard bag of candy there are a minimum of 14 individual candies, and a maximum of 22. Let \displaystyle x be the number of candies in a standard bag. Write an expression for \displaystyle x using inequalities. 

Possible Answers:

\displaystyle 14\leq x\geq 22

\displaystyle 14\geq x\geq 22

\displaystyle 13< x\leq 22

\displaystyle 14< x< 22

\displaystyle 13< x> 23

Correct answer:

\displaystyle 13< x\leq 22

Explanation:

In terms of inequalities, we know two things. \displaystyle x is greater than or equal to 14 (which is the same as \displaystyle x being greater than 13). And we know \displaystyle x is less than or equal to 22 (which is the same as \displaystyle x being less than 23).

So, we have to find the correct statement where we can find the two inequalities. We see we need  \displaystyle 14\leq x \text{ or } 13< x  and \displaystyle x\leq 22 \text{ or }x< 23.

Therefore the only answer that fits our needs is \displaystyle 13< x\leq 22.

Example Question #4 : Writing Inequalities

Write an inequality that represents the following number line.

Line

Possible Answers:

\displaystyle x>3\displaystyle x< -1

\displaystyle -1< x\leq3

\displaystyle -1\leq x< 3

\displaystyle 3< x\leq-1

\displaystyle 1\leq x\leq 3

Correct answer:

\displaystyle -1< x\leq3

Explanation:

On the number line, the graph starts at –1 and ends at 3.

The line runs between –1 and 3, so we know our inequality involves only values of x that fall between these two numbers. The open circle at –1 indicates that –1 is not included, while the shaded circle on 3 indicates that 3 is included.

\displaystyle x>-1

\displaystyle x\leq3

Combining these two inequalities into one give us our answer.

\displaystyle -1< x\leq3

Example Question #1 : Writing Inequalities

Find the solution set of the inequality:

\displaystyle 6x + 22 \leq 97

Possible Answers:

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

\displaystyle [12.5, \infty)

\displaystyle [-12.5, \infty)

\displaystyle (-\infty , 12.5]

\displaystyle (-\infty , -12.5]

Correct answer:

\displaystyle (-\infty , 12.5]

Explanation:

\displaystyle 6x + 22 \leq 97

\displaystyle 6x + 22 -22 \leq 97-22

\displaystyle 6x \leq 75

\displaystyle 6x \div 6 \leq 75\div 6

\displaystyle x \leq 12.5

or, in interval notation, \displaystyle (-\infty , 12.5]

Example Question #2 : Writing Inequalities

Find the solution set of the inequality:

\displaystyle 6x + 22 > 67

Possible Answers:

\displaystyle \left ( 7.5, \infty \right )

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

\displaystyle \left ( - \infty, 7.5 \right )

\displaystyle \left ( - \infty, -7.5 \right )

\displaystyle \left ( -7.5, \infty \right )

Correct answer:

\displaystyle \left ( 7.5, \infty \right )

Explanation:

\displaystyle 6x + 22 > 67

\displaystyle 6x + 22 -22 > 67 -22

\displaystyle 6x > 45

\displaystyle 6x \div 6 > 45\div 6

\displaystyle x > 7.5

or, in interval notation, \displaystyle \left ( 7.5, \infty \right )

Example Question #4 : Writing Inequalities

Solve for \displaystyle x:

\displaystyle 3(x + 4) \leq x - 6

Possible Answers:

\displaystyle x \leq -9

\displaystyle x \leq 3

\displaystyle x \geq -9

\displaystyle x \geq 9

\displaystyle x \leq 9

Correct answer:

\displaystyle x \leq -9

Explanation:

The first step is to distribute (multiply) through the parentheses:

\displaystyle 3(x + 4) \leq x - 6

\displaystyle 3x + 12 \leq x - 6

Then subtract \displaystyle x from both sides of the inequality:

\displaystyle 2x + 12 \leq -6

Next, subtract the 12:

\displaystyle 2x \leq -18

Finally, divide by two:

\displaystyle x \leq -9

Example Question #5 : Writing Inequalities

Solve the inequality.  \displaystyle 3x-4\leq 12x+16

Possible Answers:

\displaystyle x\leq -\frac{20}{9}

\displaystyle x\geq \frac{20}{9}

\displaystyle x\geq -\frac{20}{9}

\displaystyle x\leq -\frac{4}{3}

\displaystyle x\geq -\frac{4}{3}

Correct answer:

\displaystyle x\geq -\frac{20}{9}

Explanation:

To solve \displaystyle 3x-4\leq 12x+16, it is necessary to isolate the variable and the integers.

Subtract \displaystyle 3x and \displaystyle 16 from both sides of the equation.

\displaystyle -20\leq 9x

Divide by nine on both sides.

\displaystyle -\frac{20}{9}\leq x

This answer is also the same as:  \displaystyle x\geq -\frac{20}{9}

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