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CMA Foundation · Fundamentals of Business Mathematics and Statistics · Time and Distance

Ramesh drives from Delhi to Jaipur at 60 km/h and returns along the same route at 40 km/h. What is his average speed for the whole round trip?

His average speed is 48 km/h. For equal distances at two speeds, the average is the harmonic mean, 2×60×40 divided by 100, which equals 48. The arithmetic mean of 50 is wrong because more time is spent at the slower speed.

  1. A50 km/h
  2. B48 km/hCorrect
  3. C45 km/h
  4. D52 km/h

Explanation

For equal distances, average speed = 2xy/(x+y) = 2×60×40/100 = 48 km/h. Check: with 240 km each way, time = 4 + 6 = 10 hours and distance = 480 km, so 48 km/h. The simple mean 50 km/h is wrong because more time is spent at the lower speed.

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