A man completes a journey by car. He covers 30% of the distance at 20 km/h, 60% at 40 km/h, and the remaining 10% at 10 km/h. Wha…

Question

A man completes a journey by car. He covers 30% of the distance at 20 km/h, 60% at 40 km/h, and the remaining 10% at 10 km/h. What is his average speed?

1. A. 25 km/h (Correct answer)
2. B. 22 km/h
3. C. 12 km/h
4. D. 31 km/h

Correct Answer

Option A — 25 km/h

Detailed Solution & Explanation

The correct answer is 25 km/h.

Key Points

• For a journey split by fractions of distance at different speeds, use the weighted average speed formula:
• Average speed = Total distance ÷ Total time.
• Take the total distance as 100 km (percentages become easy). Then:
• 30 km at 20 km/h → time = 30/20 = 1.5 h
• 60 km at 40 km/h → time = 60/40 = 1.5 h
• 10 km at 10 km/h → time = 10/10 = 1 h
• Total time = 1.5 + 1.5 + 1 = 4 hours for 100 km.
• Average speed = 100 ÷ 4 = 25 km/h.
• average speed is never the simple mean of the speeds — it is total distance over total time, which weights slower stretches more heavily.

Exam Tip

• assuming total distance = 100 turns every percentage-based average-speed question into simple arithmetic.