The speed of a boat in still water is 18 km/h and the speed of the stream is 3 km/h. How much time (in hours) will it take to cover a distance of 105 km downstream and then return the same distance upstream?

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Accepted Answer

Let the speed of the boat in still water = 18 km/h. Speed of the stream = 3 km/h.

Downstream speed = (18 + 3) = 21 km/h
Upstream speed = (18 - 3) = 15 km/h

Distance to be covered each way = 105 km

Time taken downstream = Distance / Downstream speed = 105 / 21 = 5 hours
Time taken upstream = Distance / Upstream speed = 105 / 15 = 7 hours

Total time = 5 + 7 = 12 hours

Therefore, the correct answer is 12 hours.

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