UPSC Prelims 2000 · General Studies
Question 140: Basic Numeracy
A rectangular piece of iron sheet measuring 50 cm by 100 cm is rolled into a cylinder of height 50 cm. If the cost of painting the cylinder is Rs. 50 per square metre, then what will be the cost of painting the outer surface of the cylinder?
AnswerThe answer is (a).
Rolled into a cylinder of height 50 cm, the sheet has a curved surface equal to its own area, 50 cm x 100 cm = 5,000 square cm, that is 0.5 square metre. At Rs 50 a square metre the cost of painting the outer surface is 0.5 x 50 = Rs 25.
Why each option is right or wrong
- (a) Right: 0.5 square metre x Rs 50 = Rs 25.
- (b) Rs 37.50 would need 0.75 square metre of surface.
- (c) Rs 75 would need 1.5 square metres of surface.
- (d) Rs 87.50 would need 1.75 square metres of surface.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2000, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.