Question
A boat's speed in still water is 200% greater than the speed of the stream. The boat takes 13 hours to travel 180 km downstream and 66 km upstream. How much time will it take for the boat to cover a distance of 120 km downstream?
Solution
Let the speed of stream be x km/h
So, the speed of the boat in still water = x + 2x = 3x km/h
So, downstream speed = 3x + x = 4x km/h
So, upstream speed = 3x – x = 2x km/h
According to question:
180/4x + 66/2x = 13
45/x + 33/x = 13
78/x = 13
x = 78/13, x = 6
So, downstream speed = 4 × 6 = 24 km/h
So, time taken to cover 120 km downstream = 120/24 = 5 hours
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