A solid cylinder has total surface area 462 sq cm. If its curved surface area…

2016

A solid cylinder has total surface area 462 sq cm. If its curved surface area is one-third of its total surface area, then the volume of the cylinder will be

  1. A.

    639 cubic cm

  2. B.

    539 cubic cm

  3. C.

    439 cubic cm

  4. D.

    600 cubic cm

Show answer & explanation

Correct answer: B

For any solid (closed) cylinder of radius r and height h: Total Surface Area (TSA) = Curved Surface Area (CSA) + area of the two circular bases, i.e. TSA = 2πrh + 2πr2, and Volume = πr2h. Once the CSA is known as a fraction of the TSA, the base-area term 2πr2 is fixed, which pins down r, then h, then the volume.

  1. Curved Surface Area = one-third of Total Surface Area = (1/3) × 462 sq cm = 154 sq cm.

  2. Since TSA = CSA + 2πr2, the base-area term 2πr2 = 462 − 154 = 308 sq cm.

  3. Taking π ≈ 22/7: 2 × (22/7) × r2 = 308, so r2 = 49, giving r = 7 cm.

  4. From CSA = 2πrh: 154 = 2 × (22/7) × 7 × h = 44h, so h = 3.5 cm.

  5. Volume = πr2h = (22/7) × 49 × 3.5 = 539 cubic cm.

Check: CSA + 2πr2 = 154 + 308 = 462, which equals the given total surface area, and 154 is exactly one-third of 462 — confirming the radius and height obtained are consistent.

So, using π = 22/7 — the convention the clean radius value of 7 cm confirms is intended here — the volume works out to exactly 539 cubic cm.

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