Question
Downstream speed of a boat is (8/7)th of the speed of
the boat in still water. Find the time taken by the boat to cover 280 km downstream if it covers 210 km upstream in 7 hours.Solution
ATQ, Let the downstream speed of the boat and speed of the boat in still water be 8x km/hr and 7x km/hr, respectively. Therefore, speed of the stream = downstream speed - speed of the boat in still water Speed of stream Speed of stream = 8x−7x = x km/hr And, upstream speed of the boat = speed of the boat in still water - speed of stream Upstream speed Upstream speed=7x − x = 6x km/hr Given: 
So, downstream speed of the boat: 8x = 8×5 = 40km/hr Required time: 
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