UPSC Prelims 2016 · CSAT
Question 38: Basic Numeracy
A daily train is to be introduced between station A and station B starting from each end at 6 AM and the journey is to be completed in 42 hours. What is the number of trains needed in order to maintain the shuttle service ?
AnswerUPSC’s answer is (c).
Each trip takes 42 h, and a train leaves each end daily at 6 AM. A train leaving A at 6 AM reaches B 42 h later, at midnight, and can leave B only at the next 6 AM, which is 48 h after it started. The round trip then lasts 96 h = 4 days, so four trains are needed to keep a departure every 24 h. Quick check: about 2 trains are on the road in each direction, 2 + 2 = 4.
Why each option is right or wrong
- (a) Two trains cannot cover a service with a 96-hour cycle.
- (b) Three trains would leave a gap in the daily departures.
- (c) Right: a 96-hour cycle with daily departures needs 4 trains.
- (d) Seven is more than needed.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2016, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.