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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 60 km/h and 40 km/h respectively. How many seconds will they take to cross each other completely?

The trains take 9 seconds to cross. Moving in opposite directions, their speeds add to 100 km/h, which is 250/9 metres per second. The distance to clear is the sum of both lengths, 250 m, so time equals 250 divided by 250/9, giving 9 seconds.

  1. A6 seconds
  2. B9 secondsCorrect
  3. C12 seconds
  4. D15 seconds

Explanation

Relative speed in opposite directions = 60 + 40 = 100 km/h = 100 × 5/18 = 250/9 m/s. Distance to be covered = 150 + 100 = 250 m. Time = 250 ÷ (250/9) = 9 seconds. Using only one train's length (150 m) would wrongly give 5.4 s, and subtracting speeds would give a much longer time.

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