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.
back to the puzzle