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Saturday, July 26, 2008

Circling Cyclist

A cyclist drove one kilometer, with the wind in his back, in three minutes and drove the same way back, against the wind in four minutes.

The Question: If we assume that the cyclist always puts constant force on the pedals, how much time would it take him to drive one kilometer without wind?


Answer: The cyclist drives one kilometer in three minutes with the wind in his back, so in four minutes he drives 1 1/3 kilometer. Against the wind, he drives 1 kilometer in four minutes. If the wind helps the cyclist during four minutes and hinders the cyclist during another four minutes, then - in these eight minutes - the cyclist drives 2 1/3 kilometers. Without wind, he would also drive 2 1/3 kilometers in eight minutes and his average speed would then be 17.5 kilometers per hour. So it will take him 3 3/7 minutes to drive one kilometer.


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