2013 CSAT, all questions
UPSC Prelims 2013 · CSAT
Question 35: Basic Numeracy
A thief running at 8 km/hr is chased by a policeman whose speed is 10 km/hr. If the thief is 100 m ahead of the policeman, then the time required for the policeman to catch the thief will be
a2 min
b3 min
c4 min
d6 min
AnswerUPSC’s answer is (b).
The policeman gains on the thief at the difference of their speeds: 10 - 8 = 2 km/h. The gap is 100 m = 0.1 km. Time = 0.1 / 2 = 0.05 hour = 0.05 x 60 = 3 minutes. In a chase, the gap closes at the difference of the speeds, so divide the gap by that difference and watch the units.
Why each option is right or wrong
- (a) Wrong. 2 minutes would need a closing speed of 3 km/h.
- (b) Right. 0.1 km at 2 km/h takes 3 minutes.
- (c) Wrong. 4 minutes would need a closing speed of 1.5 km/h.
- (d) Wrong. 6 minutes would need a closing speed of 1 km/h.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.