Daniel Boone, Plum Creek

Daniel Boone can paddle his canoe at 15 mph in still water. He is, however, paddling on Plum Creek, which rages along at 5 mph. He paddles downriver for a while, then turns around and paddles back upstream to his starting point. What is his average speed for the entire trip?

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We make our trusty table. Note Daniel’s rates are 15 + 5 and 15 – 5.

  d = r t
down d 20 d/20
up d 10 d/10
total 2d r

d/20 + d/10

We want r:

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