# QA – Placement Quizzes | Trains, Boats and Streams | Question 15

Two trains are running in the same direction on two parallel tracks at 40 m/sec and 60 m/sec. How much time will it take to cross the slower train by faster train if the length of slower train in 50 meter and that of faster train is 20 meter? (Assume initially faster train was far behind the slower train).**(A)** 5 sec**(B)** 10 sec**(C)** 4 sec**(D)** 3.5 sec**Answer:** **(D)****Explanation:** Sol: relative speed = 60 – 40 = 20 m/sec

relative length = 70 meters

time = D/V = 70/20 = 3.5 sec

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