A bicyclist climbs a steep hill at a steady 10 miles per hour, then immediately turns around and descends the exact same route at 30 miles per hour. What was their average speed for the entire round trip?
15 mph
Average speed is total distance divided by total time (the harmonic mean of the speeds). If the hill is 30 miles long, climbing takes 3 hours (30/10) and descending takes 1 hour (30/30). Total distance is 60 miles covered in 4 hours, yielding 60 / 4 = 15 mph.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Medium. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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