Two trains of length 110 m and 90 m are running on parallel lines in the same direction at 45 km/hr and 30 km/hr respectively. In what time will the first train pass the second train?

A. 28 sec
B. 36 sec
C. 42 sec
D. 48 sec
Answer» D. 48 sec
Explanation: The trains are moving in the same direction, so their relative speed is (45-30) km/hr = 15 km/hr. We convert this speed from km/hr to m/sec by multiplying by 5/18, so relative speed = 15*(5/18) m/sec = 25/6 m/sec. The first train will have to cover a distance equal to the sum of the lengths of the two trains to pass the second train completely, which is 110 m + 90 m = 200 m. So, the time taken = Distance/Speed = 200 m / (25/6) m/sec = 48 sec.
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