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Q136 (IAS/1995) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Quantitative aptitude topics Answer Verified

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 round-trip ?

Result
Your answer: —  Â·  Correct: C
Explanation

Average speed for the whole trip is total distance divided by total time [1]. Let the one-way distance be d. Time going = d/40 and time returning = d/50, so total time = d(1/40+1/50) = 9d/200 hours. Total distance = 2d, hence average speed = (2d) / (9d/200) = 400/9 km/h ≈ 44.44 km/h. This is the harmonic-mean result for equal distances, which can be written as 2·40·50/(40+50) and matches the numeric value above. Therefore option 3 (400/9) is correct.

Sources

  1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 8: Measurement of Time and Motion > Speed = Total distance covered Total time taken > p. 114
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