Single correct option
A car travels the first half of a journey at 40 km/h and the second half, covering the same distance, at 60 km/h. The average speed for the whole journey is
- A. 48 km/h
- B. 50 km/h
- C. 52 km/h
- D. 45 km/h
Show answer and solution
Answer: (A) 48 km/h
Average speed is total distance divided by total time. For equal distances d, time is d/40 + d/60 = 5d/120, so the average speed is 2d / (5d/60) = 48 km/h. The arithmetic mean, 50 km/h, is a trap that applies only if equal times, not equal distances, were spent at each speed. The harmonic mean is the correct one here.
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