UPSC Prelims 2012 · CSAT
Question 24: Basic Numeracy
Mr. Kumar drives to work at an average speed of 48 km per hour. The time taken to cover the first 60% of the distance is 10 minutes more than the time taken to cover the remaining distance. How far is his office ?
AnswerUPSC’s answer is (b).
Let the distance be d km at 48 km/h. The first 60% takes 0.6d/48 hours and the remaining 40% takes 0.4d/48 hours. The gap is 0.2d/48 hours, which equals 10 minutes, or 1/6 hour. So d = 48/(6 x 0.2) = 40 km. Check: 24 km takes 30 minutes and the last 16 km takes 20 minutes, a difference of 10 minutes. Remember: at constant speed, the time gap is the distance gap divided by speed.
Why each option is right or wrong
- (a) Wrong. 30 km gives a time gap of 7.5 minutes, not 10.
- (b) Right. 24 km takes 30 minutes and 16 km takes 20 minutes, a 10-minute gap.
- (c) Wrong. 45 km gives a time gap of 11.25 minutes.
- (d) Wrong. 48 km gives a time gap of 12 minutes.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2012, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.