A car travels 90 km at 45 km/h and then another 90 km at 30 km/h. What is its average speed for the whole trip?
Answer and explanation
Correct answer: D. 36 km/h
- Step 1: Time for the first part = 90 ÷ 45 = 2 h; time for the second part = 90 ÷ 30 = 3 h.
- Step 2: Average speed = total distance ÷ total time = 180 ÷ 5 = 36 km/h.
Answer
36 km/h.
Why not the others: 37,5 km/h: the two speeds were averaged without weighting by time. 180 km/h: this is the total distance. 42,5 km/h: the simple average of the speeds.
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