UPSC Prelims 2018 · CSAT
Question 6: Basic Numeracy
A train 200 metres long is moving at the rate of 40 kmph. In how many seconds will it cross a man standing near the railway line?
AnswerUPSC’s answer is (d).
To pass a man standing still, the train must cover only its own length, 200 m. Convert the speed: 40 km/h × 5/18 = 100/9 m/s. Time = distance ÷ speed = 200 ÷ (100/9) = 18 seconds. Remember the rule: for a point (a man, a pole) the distance is the train's length; for a platform or bridge, add that length as well.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) 12 s would need about 16.7 m/s, which is 60 km/h.
- (b) 15 s would need about 13.3 m/s, which is 48 km/h.
- (c) 16 s would need 12.5 m/s, which is 45 km/h.
- (d) Correct: 200 m at 100/9 m/s takes 18 s.
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.