A car travels from point A to B at 20 kmph and travels back from B to A at 60…
2026
A car travels from point A to B at 20 kmph and travels back from B to A at 60 kmph. Find the average speed of the car.
- A.
30 km/h
- B.
50 km/h
- C.
35 km/h
- D.
5 km/h
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Show answer & explanation
Correct answer: A
Key idea: for equal distances, the average speed is the harmonic mean of the two speeds: 2ab/(a+b).
Step 1: Let each one-way distance be d. Time to go = d/20 hours; time to return = d/60 hours.
Step 2: Total distance = 2d. Total time = d/20 + d/60 = d/15 hours.
Step 3: Average speed = total distance ÷ total time = 2d ÷ (d/15) = 30 km/h.
Using the harmonic-mean formula directly: 2 × 20 × 60 ÷ (20 + 60) = 2400 ÷ 80 = 30 km/h.
Answer: 30 km/h