WAEC 2018 Mathematics · Question 9
The volume of a cylindrical tank, 10m high is 385 m. Find the diameter of the tank. [Take ]
Options
- A.14m
- B.10m
- C.7m
- D.5m
Answer: C. 7m
Explanation written with AI and checked against the answer key
Analyze the question: We have a cylinder with height h = 10 m and volume V = 385 (the unit is written as m², but volume should be m³, so this is a typo in the question). We need the diameter. Concept: Volume of a cylinder: V = πr²h Solution: 385 = (22/7) × r² × 10 r² = (385 × 7) / (22 × 10) r² = 2695 / 220 r² = 12.25 r = 3.5 m Diameter = 2r = 2 × 3.5 = 7 m Check: (22/7) × 3.5² × 10 = (22/7) × 12.25 × 10 = 22 × 1.75 × 10 = 385 ✓ Tip: Always read the question for what is asked. Here, you find the radius first, but the question wants the diameter, so remember to double it. Many students lose marks by stopping at r = 3.5 (not an option here, but a common trap). Also, with π = 22/7, look for factors of 7 and 11 to cancel quickly: 385 = 7 × 5 × 11.AI can make mistakes. Report anything that looks wrong.
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