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      Question

      Train A when travelling with a speed of 144 km/h crosses

      a pole in 6 seconds. Find the time taken by the train A to cross another train B of length 25% more than that of train A which is coming from the opposite direction with a speed of 126 km/h.
      A 6.8 seconds Correct Answer Incorrect Answer
      B 7.2 seconds Correct Answer Incorrect Answer
      C 7.5 seconds Correct Answer Incorrect Answer
      D 8 seconds Correct Answer Incorrect Answer

      Solution

      Speed of train A = 144 × 5/18 = 40 m/s
      Length of train A = 40 × 6 = 240 metres
      Length of train B = 1.25 × 240 = 300 metres
      Speed of train B = 126 × 5/18 = 35 m/s
      Relative speed = 40 + 35 = 75 m/s (opposite direction)
      Total distance = 240 + 300 = 540 metres
      Desired time = 540/75 = 7.2 seconds

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