QA – Placement Quizzes | Trains, Boats and Streams | Question 1

A boatman takes 3 hours 45 minutes to travel 15 km downstream and takes 2 hours 30 minutes to travel 5 km upstream of a river. What is the speed of the stream of the river in km/h?
(A) 2 km/h
(B) 1 km/h
(C) 6 km/h
(D) 4 km/h

Answer: (B)
Explanation: Downstream:
Time taken = 3 + 45/60 = 3 + 3/4 = 15/4 h.
Distance covered = 15 km.
Downstream Speed = 15 / (15/4) = 4 km/h.
Upstream:
Time taken = 2 + 30/60 = 2 + 1/2 = 5/2 h.
Distance covered = 5 km.
Upstream Speed = 5 / (5/2) = 2 km/h.
We know, speed of stream = 1/2 (Downstream Speed – Upstream Speed) = 1/2 (4-2) = 1 km/h.

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