WAEC 2021 Mathematics · Question 40

The distance d between two villages east more than 18 KM but not more than 23KM. which of these inequalities represents the statements?

Options

  1. A.18 ≤ d ≤ 23
  2. B.18 < d < 23
  3. C.18 ≤ d < 23
  4. D.18 < d ≤ 23

Answer: D. 18 < d ≤ 23

Explanation written with AI and checked against the answer key

Analyze the question

The distance d is described by two conditions:

  1. "More than 18 km" means d is greater than 18, written d > 18. It does not include 18.
  2. "Not more than 23 km" means d cannot go above 23, written d ≤ 23. It does include 23.

Concept

  • "More than" means strictly greater (>).
  • "Not more than" means less than or equal to (≤).
  • "At least" means ≥, and "less than" means <.

Solution

Combine the two conditions:

  • d > 18
  • d ≤ 23

Together: 18 < d ≤ 23

Check against the options

  • A. 18 ≤ d ≤ 23: wrong, because it includes 18.
  • B. 18 < d < 23: wrong, because it excludes 23, but "not more than 23" allows exactly 23.
  • C. 18 ≤ d < 23: wrong, because it includes 18 and excludes 23, the opposite of what is needed.
  • D. 18 < d ≤ 23: correct, because it excludes 18 and includes 23.

Exam tip

Translate each phrase on its own.

  • "More than" or "less than" gives a strict sign (< or >).
  • "Not more than" or "not less than" gives a sign with "or equal to" (≤ or ≥).

"Not more than 23" means 23 is the largest allowed value, so 23 itself is included.

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