A car drives the first half of a journey at 20 km/h and the second half (the same distance) at 30 km/h. What is its average speed for the whole journey?
Answer and explanation
Correct answer: B. 24 km/h
- Step 1: Let each half be d. The total time is d/v1 + d/v2 and the total distance is 2d.
- Step 2: Average speed = 2 x 20 x 30 / (20+30) = 24 km/h.
Answer
24 km/h.
Why not the others: 25 km/h: the speeds were averaged, but the times spent are different. 12 km/h: the factor 2 is missing. 10 km/h: the speeds were subtracted.
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