A commuter travels to campus at 40 km/h and returns along the same route at 60 km/h. What is the average speed for the round trip?
Answer and explanation
Correct answer: D. 48 km/h
- Step 1: For equal distances, average speed is the harmonic mean: (2 v1 v2) / (v1 + v2). Step 2. (2 40 60) / (40 + 60) = 4800 / 100 = 48 km/h. Answer: 48 km/h. Why not the others: 50 km/h is the arithmetic mean, which is flawed because more time is spent at the slower speed.
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