NECO 2001 Mathematics · Question 26
The surface area of a sphere is 616m2. what is the volume of-the sphere (correct to two significant figures)? (take π = 3.142)
Options
- A.14 cm
- B.210 cm
- C.1,400 cm
- D.2,100 cm
- E.4,300 cm
Answer: C. 1,400 cm
Explanation written with AI and checked against the answer key
Analyze the question: We are given the surface area of a sphere (616) and asked for its volume to 2 significant figures, using π = 3.142.
Concept:
- Surface area = 4πr²
- Volume = (4/3)πr³
Solution:
Step 1: Find r. 4πr² = 616 r² = 616 / (4 × 3.142) = 616 / 12.568 = 49.014... r ≈ 7.001
So r ≈ 7 (the question was clearly designed with π = 22/7, giving r = 7 exactly).
Step 2: Find the volume. V = (4/3) × π × r³ r³ ≈ 343.2 (using r ≈ 7.001) V = (4/3) × 3.142 × 343.2 V ≈ 4.1893 × 343.2 ≈ 1437.8
Using r = 7 exactly gives V = 4.1893 × 343 ≈ 1437.0
To 2 significant figures: 1,400
Note on units: The question states the area in m² but the options are in cm³. This is a typo in the question. The numerical value is what matters, and the answer matches option C.
Answer: C. 1,400 (cm³)
Tip: When the surface area is a multiple of 22/7 values (like 616 = 4 × 22/7 × 49), expect a neat radius like 7. Check by working out 616 ÷ 88 = 7 (since 4 × 22/7 = 88/7, so r² = 616 × 7 / 88 = 49). Also, always check the units in the question and options, since typos happen.
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