WAEC 2023 Mathematics · Question 1
The radius and height of a solid cylinder is 8 cm and 14 cm respectively. Find, correct to two d.p the total surface area. (Take
Options
- A.
- B.
- C.
- D.
Answer: A.
Explanation written with AI and checked against the answer key
Analyze the question: We need the total surface area of a closed solid cylinder with r = 8 cm and h = 14 cm, using π = 22/7.
Concept: Total surface area of a cylinder = 2πr(h + r), which is the curved surface (2πrh) plus the two circular ends (2πr²).
Solution:
- 2πr(h + r) = 2 × (22/7) × 8 × (14 + 8)
- = 2 × (22/7) × 8 × 22
- = (2 × 22 × 8 × 22) / 7
- = 7744 / 7
- = 1106.285714...
Correct to 2 d.p.: 1,106.29 cm²
Check using the separate parts:
- Curved surface: 2 × (22/7) × 8 × 14 = 704 cm²
- Two circular ends: 2 × (22/7) × 64 = 1408/7 ≈ 201.29 cm²
- Total: 704 + 201.29 = 905.29 cm²
That doesn't match, so let me recheck. 2πrh = 2 × (22/7) × 8 × 14 = 2 × 22 × 8 × 2 = 704. Correct. The ends: 2πr² = 2 × (22/7) × 64 = 2816/7 ≈ 402.29 cm² (I previously miscalculated 1408/7, which is only one end).
Total: 704 + 402.29 = 1,106.29 cm² ✔
Answer: Option A, 1,106.29 cm²
Tip: Factor first: 2πr(h + r). Here h + r = 22, which cancels neatly with the 7 pattern of π = 22/7 and saves time. Also, watch out for "total" vs "curved" surface area: total includes both circular ends.
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