Question
The downstream speed of a boat is 6 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 10:3. Find the total time taken by boat to travel 39 km downstream and 28 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) = 6 ⇒  y = 3 km/hr ⇒  x = 3 × 10/3 = 10 km/hr Required time = [39/(10+3)] + [28/(10−3)] = 7 hr
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