Question
The downstream speed of a boat is 4 km/hr more than its
upstream speed and the ratio of the speed of the boat in still water to the speed of the stream is 11:2. Find the total time taken by boat to travel 52 km downstream and 45 km upstream?Solution
Let the speed of boat in still water be x km/hr and that of stream be y km/hr. ATQ, ⇒  (x + y) – (x – y) = 4 ⇒  y = 2 km/hr ⇒  x = 2 × 11/2 = 11 km/hr Required time = [52/(11+2)] + [45/(11−2)] = 9 hr
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