Question
A boat covers 30 km downstream in 60 minutes. If the
ratio of the speed of the boat in still water to that of the speed of the stream is 8:4, respectively, then find the time taken by the boat to cover a distance of 15 km upstream.Solution
ATQ, Speed of the boat downstream = (30/60)×60 = 30 km/h Let the speed of the boat in still water = 8x km/h Speed of stream = 4x km/h Speed of the boat downstream = 8x+4x = 12x km/h 30 = 12x x = 2.5 Speed of the boat in still water = 8×2.5 = 20 km/h Speed of the stream = 4×2.5 = 10 km/h Speed of the boat upstream = 20−10 = 10 km/h Time taken by the boat to cover the distance of 15 km upstream = (15/10)×60 = 90 minutes
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