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Mathematics

Inequalities (linear and compound) — ACT practice questions

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What this topic is

Inequalities (linear and compound) are solved much like equations, with one key difference: multiplying or dividing both sides by a negative number reverses the inequality sign.

A compound inequality, such as x plus one lying between negative two and five, is solved by doing the same step to all three parts at once. Absolute value inequalities describe distance, so all numbers within two units of six are exactly those where the absolute value of x minus six is at most two.

Questions ask for solution sets, number-line graphs or the first whole number meeting a condition; choices often differ only by a flipped sign or a strict versus inclusive symbol.

Sample questions

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Question 1Easier

Which of the following is the solution of −5<3x+1≤13?

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Answer: A — −2<x≤4

Subtracting 1 gives −6<3x≤12. Dividing all three parts by 3 gives −2<x≤4.

Question 2Easier

Which of the following inequalities represents all real numbers m whose distance from 50 is at most 3?

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Answer: A — ∣m−50∣≤3

The expression ∣m−50∣ is the distance from m to 50. Requiring that distance to be at most 3 gives ∣m−50∣≤3.

Question 3Mid

A collector’s display case holds 12 coins in its first row. Each row after that holds 7 more coins than the row before it. Which row is the first to contain more than 100 coins?

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Answer: C — 14

Row n holds 12+7(n−1) coins. Row 13 holds 12+7(12)=96 coins, and row 14 holds 12+7(13)=103 coins, the first total exceeding 100.

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