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
- A.18 ≤ d ≤ 23
- B.18 < d < 23
- C.18 ≤ d < 23
- 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:
- "More than 18 km" means d is greater than 18, written d > 18. It does not include 18.
- "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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