2015 CSAT, all questions
UPSC Prelims 2015 · CSAT
Question 34: Basic Numeracy
In a 500 metres race, B starts 45 metres ahead of A, but A wins the race while B is still 35 metres behind. What is the ratio of the speeds of A to B assuming that both start at the same time ?
a25 : 21
b25 : 20
c5 : 3
d5 : 7
AnswerUPSC’s answer is (a).
In the same time, A covers the full 500 m. B starts 45 m ahead, so B has 455 m to run; B is 35 m short of the finish when A finishes, so B has run 455 − 35 = 420 m. Speeds are in the ratio of distances covered in equal time: A : B = 500 : 420 = 25 : 21.
Why each option is right or wrong
- (a) Right: 500 : 420 = 25 : 21.
- (b) Wrong: 25 : 20 = 500 : 400 would mean B ran 400 m.
- (c) Wrong: 5 : 3 would mean B ran 300 m.
- (d) Wrong: 5 : 7 would make B faster than A, but A wins.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2015, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.