A man drives 150 km from A to B in 3 hr and 20 mins , and returns to the place…

2023

A man drives 150 km from A to B in 3 hr and 20 mins , and returns to the place in 4 hr and 10 mins , If 'S' is the average speed of the entire trip then the average speed for the journey from A to B exceeds 'S' by

  1. A.

    5.5

  2. B.

    6

  3. C.

    5

  4. D.

    4.5

Attempted by 43 students.

Show answer & explanation

Correct answer: C

Answer: 5

  1. Distance from A to B = 150 km.

  2. Time from A to B = 3 hr 20 min = 10/3 hr. Speed A to B = 150 ÷ (10/3) = 45 km/h.

  3. Time from B to A = 4 hr 10 min = 25/6 hr. Speed B to A = 150 ÷ (25/6) = 36 km/h.

  4. Average speed for the entire round trip (equal distances) is the harmonic mean: 2 × 45 × 36 ÷ (45 + 36) = 40 km/h. (Equivalently total distance 300 km ÷ total time 7.5 h = 40 km/h.)

  5. Difference: speed from A to B − overall average = 45 − 40 = 5 km/h.

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