A car covers 40% of a certain distance at a pace of 20 km/h and the remaining distance at a pace of 30 km/h. What is the average…

Question

A car covers 40% of a certain distance at a pace of 20 km/h and the remaining distance at a pace of 30 km/h. What is the average speed of the car for the entire journey?

1. A. 24 km/h
2. B. 25 km/h (Correct answer)
3. C. 26 km/h
4. D. 27 km/h

Correct Answer

Option B — 25 km/h

Detailed Solution & Explanation

The correct answer is 25 km/h.

Key Points

• Take the total distance as 100 km to keep the arithmetic clean:
  • First leg: 40 km at 20 km/h → time = 2 hours
  • Second leg: 60 km at 30 km/h → time = 2 hours
• Total time = 4 hours for 100 km.
• Average speed = 100 ÷ 4 = 25 km/h.

Additional Information

• Average speed is total distance ÷ total time, never the plain average of the speeds — that would give 25 here only by coincidence of the chosen figures.
• For equal distances at speeds a and b, the average is the harmonic mean 2ab/(a + b); for equal times, it is the ordinary average (a + b)/2.
• Assuming a convenient total distance is always safe when the question gives only proportions, since the average speed does not depend on the actual distance.

प्रश्न (हिन्दी में)

एक कार एक निश्चित दूरी का 40% भाग 20 किमी/घंटा की गति से तथा शेष दूरी 30 किमी/घंटा की गति से तय करती है। पूरी यात्रा के दौरान कार की औसत गति क्या है?

1. A. 24 किमी/घंटा
2. B. 25 किमी/घंटा
3. C. 26 किमी/घंटा
4. D. 27 किमी/घंटा