CMA Foundation · Fundamentals of Business Mathematics and Statistics · Measures of Central Tendency and Dispersion
Ravi drives 60 km from Pune to a town at 30 km/h and returns the same 60 km at 60 km/h. What is his average speed for the whole round trip?
The average speed is 40 km/h. For equal distances the harmonic mean of 30 and 60 applies: 2×30×60/90 = 40. Equivalently, 120 km is covered in 3 hours. The arithmetic mean of 45 is wrong because more time is spent at the slower speed.
- A45 km/h
- B40 km/hCorrect
- C50 km/h
- D36 km/h
Explanation
Equal distances call for the harmonic mean: 2 × 30 × 60 / (30 + 60) = 3600/90 = 40 km/h. Check: total time = 2 h + 1 h = 3 h, and 120/3 = 40. The value 45 is the arithmetic mean, which ignores the extra time spent at the lower speed.
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