NECO 2004 Mathematics · Question 29
Find the surface area of a sphere whose radius is 3.5cm, correct your answer to one decimal place (π = )
Options
- A.12.8cm2
- B.25.7cm2
- C.77.0cm2
- D.154.0cm2
- E.179.7cm2
Answer: D. 154.0cm2
Explanation written with AI and checked against the answer key
Analyze the question: We need the surface area of a sphere with radius 3.5 cm. Concept: Surface area of a sphere = 4πr² Note on π: The question says π = 22/5, which is almost certainly a typo. The standard value used in these questions is π = 22/7. Let me show both, so you see why. Solution with π = 22/7: A = 4 × (22/7) × (3.5)² A = 4 × (22/7) × 12.25 A = 4 × 22 × 1.75 (since 12.25 ÷ 7 = 1.75) A = 88 × 1.75 A = 154.0 cm² Check with π = 22/5 as literally written: A = 4 × 4.4 × 12.25 = 215.6 cm² This is not among the options, so the intended value must be 22/7. That gives 154. Answer: D, 154.0 cm² Tip: When the radius is 3.5 (or a multiple of 7 halved), use π = 22/7, because the 7 cancels neatly. Also, if your answer does not match any option, check whether the question has a typo in the given value of π. Remember that the surface area is 4πr², while the volume is (4/3)πr³.AI can make mistakes. Report anything that looks wrong.
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