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 5:2. Find the total time taken by boat to travel 42 km downstream and 30 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 × 5/2 = 5 km/hr Required time = [42/(5+2)] + [30/(5−2)] = 16 hr
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