A car drives 240 km at 80 km/h and returns the same 240 km at 60 km/h. What is its average speed over the whole trip?
Answer and explanation
Correct answer: C. 68.5714 km/h
- Step 1: Total time = 240/80 + 240/60 = 7 h. Step 2. Average speed = 480 / 7 = 68.5714 km/h. Answer: 68.5714 km/h. Why not the others: 70 km/h: the simple average of the speeds was used. 140 km/h: the speeds were added. 34.2857 km/h: only one leg of the distance was used.
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