UPSC Prelims 2018 · CSAT
Question 40: Basic Numeracy
Two persons, A and B are running on a circular track. At the start, B is ahead of A and their positions make an angle of 30° at the centre of the circle. When A reaches the point diametrically opposite to his starting point, he meets B. What is the ratio of speeds of A and B, if they are running with uniform speeds?
AnswerUPSC’s answer is (a).
Both run in the same direction, with B ahead of A by 30°. When A has covered half the track, 180°, he meets B at the diametrically opposite point. B started 30° ahead of A, so B has covered only 180° - 30° = 150° in the same time. With uniform speeds the speed ratio equals the distance ratio: 180 : 150 = 6 : 5.
Why each option is right or wrong
- (a) Correct: A covers 180° while B covers 150°.
- (b) 4 : 3 would mean B covers 135° while A covers 180°.
- (c) 6 : 1 would mean B covers only 30°.
- (d) 4 : 2 is 2 : 1, which would mean B covers 90°.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2018, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.