Multiple choice

A bike rider covers the four sides of square field at speeds 20, 40, 60 and 80 kmph. then the average speed of the bike in the entire journey is/एक बाइक सवार वर्गाकार खेत की चार भुजाओं को क्रमशः 20, 40, 60 और 80 किमी./घंटा की चाल से तय करता है तो सम्पूर्ण यात्रा में बाइक की औसत गति है-

  1. 60 kmph/किमी./घण्टा

  2. 40 kmph/किमी./घण्टा

  3. 50 kmph/किमी./घण्टा

  4. 38.4 kmph/किमी./घण्टा
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D Correct answer
Explanation

For average speed with varying speeds over equal distances, use harmonic mean. Average speed = 4 / (1/20 + 1/40 + 1/60 + 1/80) = 4 / (0.05 + 0.025 + 0.0167 + 0.0125) = 4 / 0.1042 ≈ 38.4 kmph. The key insight is that equal distances mean time-based averaging (harmonic mean), not arithmetic mean.

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