A person travelled from one place to another at an average speed of 40 kilometres/hour and back to the original place at an average speed of 50 kilometres/hour. What is his average speed in kilometres/hour during the entire roundtrip?
Reviewed by Dalvoy
UPSC Civil Services preparation
- A45
- B20
- C400/9Correct
- DImpossible to find out unless the distance between the two places is known
Explanation
To find the average speed for a round trip where the distance for both journeys is the same, we use the Harmonic Mean formula: Average Speed = (2xy) / (x + y), where x and y are the two speeds.
In this case, x = 40 km/h and y = 50 km/h.
Plugging the values into the formula:
Average Speed = (2 * 40 * 50) / (40 + 50)
Average Speed = 4000 / 90
Average Speed = 400 / 9
The distance is not required because it cancels out in the calculation. Therefore, option C is the correct answer.
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