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    Question

    Train A when travelling with a speed of 72 km/h crosses

    a pole in 12 seconds. Find the time taken by the train A to cross another train B of length 40% more than that of train A which is coming from the opposite direction with a speed of 108 km/h.
    A 10.8 seconds Correct Answer Incorrect Answer
    B 11.52 seconds Correct Answer Incorrect Answer
    C 12.4 seconds Correct Answer Incorrect Answer
    D 13 seconds Correct Answer Incorrect Answer

    Solution

    Speed of train A = 72 × 5/18 = 20 m/s
    Length of train A = 20 × 12 = 240 metres
    Length of train B = 1.4 × 240 = 336 metres
    Speed of train B = 108 × 5/18 = 30 m/s
    Relative speed = 20 + 30 = 50 m/s (opposite direction)
    Total distance = 240 + 336 = 576 metres
    Desired time = 576/50 = 11.52 seconds

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