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 7:2. Find the total time taken by boat to travel 36 km downstream and 25 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 × 7/2 = 7 km/hr Required time = [36/(7+2)] + [25/(7−2)] = 9 hr
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