Multiple choice

A student reached his school late by 20 minutes by travelling at a speed of 9 km/hr Had he travelled at the speed of 12 km/hr he would have reached his school 20 minutes early Find the distance between his house and the school?

  1. 12 km

  2. 6 km

  3. 3 km

  4. 24 km
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let distance be D. Time taken at 9 km/hr is D/9 and at 12 km/hr is D/12. The difference in time is 40 minutes (20 late + 20 early), which is 2/3 hours. Solving D/9 - D/12 = 2/3 gives D/36 = 2/3, so D = 24 km.

AI explanation

Let the distance be d km; using the formula distance equals speed multiplied by time, we write d/9 - d/12 = 40/60 since the total time difference between being 20 minutes late and 20 minutes early is 40 minutes. Finding a common denominator gives (4d - 3d) / 36 = 2/3, which simplifies to d/36 = 2/3. Solving this gives d = 24 km.

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