UPSC Prelims 2003 · General Studies
Question 49: Basic Numeracy
‘A’ walks around a circular field at the rate of one round per hour while ‘B’ runs around it at the rate of six rounds per hour. They start in the same direction from the same point at 7.30 a.m. They shall first cross each other at
AnswerThe answer is (d).
Both start together in the same direction, so B gains on A at the relative speed of 6 - 1 = 5 rounds per hour. B first meets A when B has gained one full round: 1/5 hour = 12 minutes. Starting at 7.30 a.m., they first cross at 7.42 a.m. Had they run in opposite directions, the relative speed would be 7 rounds per hour and they would meet after about 8.6 minutes.
Why each option is right or wrong
- (a) 8.30 is a full hour later; B gains a round in only 12 minutes.
- (b) 8.10 is 40 minutes after the start, which is too late.
- (c) 7.48 is 18 minutes after the start, not 12.
- (d) Correct: 12 minutes after 7.30.
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.