Suppose there is a river that has no current. A man gets into a canoe and paddles upstream from his dock to the river’s bend 5 kilometres away, and then turns around and returns to the dock. The entire trip takes 40 minutes. Now suppose that the river has a current of 2 kilometres per hour. If the man makes exactly the same trip, will it take longer than 40 minutes, shorter than 40 minutes, or the same amount of time?
Answer
The trip will take longer than 40 minutes. The man will travel two kph slower on the upstream trip and two kph faster on the downstream trip. However, the trip will take longer than 40 minutes because the canoe will be slowed down for a longer period of time going upstream than the time it gains going downstream.
