Q.14: Two persons are walking beside a railway track at respective speeds of 2 and 4 km per hour in the same direction. A train came from behind them and crossed them in 90 and 100 seconds, respectively. The time, in seconds, taken by the train to cross an electric post is nearest to
Correct Answer: 82
Two person to be A and B
A = 2km/hr and B = 4 km/hr
Speed of the train = t km/hr
Given, Train crosses A in 90 seconds (Length of the train is the distance)
t – 2 in 90 seconds and t – 4 in 100 seconds
Ratio of speed is opposite to time
(t – 2) 90 = (t – 4) 100
Solving t = 22km/hr
For A, Speed = t – 2 = 20 km/hr in 90 seconds
So travelling at 22 km/hr —-> 90×20 / 22 ≅ 82
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