Multiple choice general knowledge math & puzzles

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.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?

  1. 24/7

  2. 23/7

  3. 22/7

  4. 21/7
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A Correct answer
Explanation

Let cyclist speed = c km/min and wind speed = w km/min. With wind: c + w = 1/3 km/min (covers 1 km in 3 min). Against wind: c - w = 1/4 km/min (covers 1 km in 4 min). Adding these: 2c = 7/12, so c = 7/24 km/min. Without wind, time = distance/speed = 1/(7/24) = 24/7 minutes.

AI explanation

Let c be the cyclist's speed on still air and w the wind speed (both in km/min). With the wind: c+w = 1/3; against the wind: c-w = 1/4. Adding these gives 2c = 7/12, so c = 7/24 km/min. The time to cover 1 km without wind is the reciprocal of that speed, which works out to 24/7 minutes.

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