UPSC Prelims 2003 · General Studies
Question 57: Basic Numeracy
Four different candles, which can last for 5 hours, 4 hours, 3 hours and 2 hours of burning, respectively, are lit in a room at the same instant and allowed to burn till such time that the three candles in the room get extinguished. The cost of burning each one of these candles is 75 paise per hour. The cost involved is:
AnswerThe answer is (c).
The candles last 5, 4, 3 and 2 hours, and they burn until three of them have gone out, which happens when the 4-hour candle finishes at the 4-hour mark. Burning time: the 5-hour candle burns for 4 hours, the 4-hour candle for 4, the 3-hour candle for 3 and the 2-hour candle for 2, a total of 13 candle-hours. At 75 paise per hour, the cost = 13 x 0.75 = Rs 9.75.
Why each option is right or wrong
- (a) Rs 2.75 does not correspond to 13 candle-hours at 75 paise.
- (b) Rs 3.75 is only 5 candle-hours, which is too few.
- (c) Correct: 13 x 0.75 = Rs 9.75.
- (d) Rs 12.50 is not 75 paise times the total burning hours.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2003, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.