UPSC Prelims 2022 · CSAT
Question 46: Basic Numeracy
A man started from home at 14:30 hours and drove to village, arriving there when the village clock indicated 15:15 hours. After staying for 25 minutes, he drove back by a different route of length 1·25 times the first route at a rate twice as fast reaching home at 16:00 hours. As compared to the clock at home, the village clock is
AnswerUPSC’s answer is (d).
Let the first trip take t minutes in real time. The return route is 1.25 times as long at twice the speed, so it takes 1.25/2 = 0.625t. By the home clock, 14:30 to 16:00 is 90 minutes = t + 25 + 0.625t, so 1.625t = 65 and t = 40. He reached the village at 15:10 by the home clock, but the village clock showed 15:15, so the village clock is 5 minutes fast.
Why each option is right or wrong
- (a) Wrong: a slow clock would show earlier than 15:10, but it shows 15:15.
- (b) Wrong: it reads 5 minutes ahead, not behind.
- (c) Wrong: the gap is 5 minutes, not 10.
- (d) Correct: village clock 15:15 against true time 15:10.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2022, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.