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CMA Foundation · Fundamentals of Business Mathematics and Statistics · Time and Distance

Two trains, 150 m and 100 m long, run on parallel tracks in opposite directions at 54 km/h and 36 km/h respectively. How many seconds do they take to cross each other completely?

They take 10 seconds. Moving in opposite directions, their relative speed is 54 + 36 = 90 km/h, or 25 m/s. The total distance to clear is 150 + 100 = 250 m, so time is 250 divided by 25, which is 10 seconds.

  1. A8 seconds
  2. B12 seconds
  3. C10 secondsCorrect
  4. D15 seconds

Explanation

Relative speed in opposite directions = 54 + 36 = 90 km/h = 25 m/s. Distance to cover = 150 + 100 = 250 m. Time = 250/25 = 10 seconds. Using the difference of speeds (18 km/h = 5 m/s) would wrongly give 50 seconds.

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