A car drives the first half of a journey at 80 km/h and the second half (the same distance) at 120 km/h. What is its average speed for the whole journey?
Answer and explanation
Correct answer: A. 96 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 80 x 120 / (80+120) = 96 km/h.
Answer
96 km/h.
Why not the others: 100 km/h: the speeds were averaged, but the times spent are different. 48 km/h: the factor 2 is missing. 40 km/h: the speeds were subtracted.
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