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.
Therefore, it will take him 3 3/7 minutes to drive one kilometer.
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