Question 146665: A man in a canoe is paddling upstream. He passes a floating log(going downstream) at the Elk's Lodge. He continues to paddle for 90 more miutes, before turning around to go downsteam. The canoer reaches the log again at the sewer plant which is exactly 1 mile from the Elk's lodge. At what rate is the river flowing?
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! This is a hard problem unless you take the right perspective.
The canoe and the log are both in the river and moving at the same speed relative to the land (the speed of the river). Because of that, we know that it takes the same time, 90 minutes, to overtake the log as he rowed away from it.
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If that's unclear, envision the same event in open water with no land visible, whether the water is moving or not. If you row away from something for 90 minutes, it will take 90 minutes to get back to it.
So, his round trip time was 180 minutes, and during that time, the log moved 1 mile. That makes the speed of the river 1/3 mph.
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