Question
A boat can cover 84 km in upstream in 2 hours, if the
speed of the stream is 30% of the speed of boat in still water, then find the time taken by the boat to cover 156 km in downstream.Solution
Let the speed of boat in still water be ‘x’ km/h
Speed of stream = 0.30 × x = ‘0.3x’ km/h
Speed of boat in upstream = x – 0.3x = 0.7x km/h
So, 0.7x = 84/2
Or, 0.7x = 42
Or, x = 60
So, speed of boat in still water = 60 km/h
And, speed of stream = 60 × 0.3 = 18 km/h
Time required to cover 156 km in downstream = {156/(18 + 60)} = 2 hours
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