Let's say I coast down a hill near my house at 20 mph and return at 10 mph. What's my average speed on the hill?
No. The answer is not 15 mph.
Mathematics Problems and Warm-ups at the University of Minnesota poses “The Baffling Bicycle” as Problem #71. It says:
“A bicycle climbs a certain hill at 10 miles per hour and returns at 20 miles per hour. What is its average speed for the entire trip?
“The apparent answer — 15 miles per hour — is wrong. The correct answer is 13 1/3 miles per hour because speed is determined by dividing the distance by time. Notice, incidentally, that the answer is the same no matter how long the hill is.”
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