Multiple choice general knowledge science & technology

A motorist wishes to travel 40 kilometers at an average speed of 40 km/hr. During the first 20 kilometers, an average speed of 40 km/hr is maintained. During the next 10 kilometers, however, the motorist goofs off and averages only 20 km/hr. To drive the last 10 kilometers and average 40 km/hr, the motorist must drive

  1. 60 km/hr

  2. 80 km/hr

  3. 90 km/hr

  4. faster than the speed of light
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

To average 40 km/hr over 40 km, you must complete the trip in exactly 1 hour. But you already spent 30 minutes on the first 20 km (20/40 hr) plus 30 minutes on the next 10 km (10/20 hr), totaling 60 minutes. You have zero time left to cover the remaining 10 km, which is impossible.

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