Question
A boat can travel at 12 km/h in still water. The speed
of the stream is 3 km/h. How much time will it take for the boat to go from point A to point B and come back, if the distance between A and B is 30 km?Solution
Speed downstream = 12 + 3 = 15 km/h Speed upstream = 12 − 3 = 9 km/h Time downstream = distance / speed = 30 / 15 = 2 hours Time upstream = 30 / 9 = 10/3 hours ≈ 3 hours 20 minutes Total time = 2 + 10/3 = (6 + 10)/3 = 16/3 hours = 5 hours 20 minutes.
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