Multiple choice

A Bike travels the first 1/4 of a certain distance with speed of 10km/hr, the second 1/4 distance with a speed of 20km/hr , the third 1/4 distance with a speed of 30km/hr and the last 1/4 distance with a speed of 40km /hr the average speed of the bike for whole journey is-

  1. 15.8 km/hr.

  2. 18.5 km/hr.

  3. 19.2 km/hr.

  4. 17.2 km/hr.

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let each quarter = d km. Time for each quarter = d/10 + d/20 + d/30 + d/40 = d(12/120 + 6/120 + 4/120 + 3/120) = 25d/120. Total distance = 4d. Average speed = 4d / (25d/120) = 480d/25d = 19.2 km/hr.

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