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 (in kmph )-

  1. 60 kmph

  2. 40 kmph

  3. 50 kmph

  4. 38.4 kmph
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For equal distances, average speed is harmonic mean of speeds: 4/(1/20+1/40+1/60+1/80) = 4/(12/240+6/240+4/240+3/240) = 4/(25/240) = 4×240/25 = 38.4 kmph.

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