Total surface of a cylinder — Mensuration Aptitude Question
Total surface of a cylinder: What is the total surface area of a closed cylinder with radius 7 cm and height 3 cm? Answer and worked solution on CodeKairo.
- Topic: Mensuration
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 75 seconds
Question
What is the total surface area of a closed cylinder with radius 7 cm and height 3 cm? (Take π = 22/7.)
Options
- 308 cm²
- 396 cm²
- 440 cm²
- 484 cm²
Show the answer and the worked solution
Correct answer: C. 440 cm²
Worked solution
- Total surface = 2πr(r + h) = 2 × (22/7) × 7 × (7 + 3).
- 2 × (22/7) × 7 = 44.
- 44 × 10 = 440 cm².
Answer: 440 cm².
The idea
Total surface adds the two circular ends to the curved surface: 2πrh + 2πr² = 2πr(r + h).
Shortcut. With r = 7 and π = 22/7, 2πr is exactly 44, so the answer is 44 × (r + h) = 44 × 10 = 440 cm².
Common trap. "308 cm²" — the two circular ends alone (2 × 154 cm²), leaving out the curved surface of 132 cm².