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    Question

    A train can cross a bridge and a pole in 9 seconds and 6

    seconds respectively. The length of the bridge is 90 metres. Find the time taken by train to cross a van which is running in the same direction with a speed of 15 m/sec.
    A 10 seconds Correct Answer Incorrect Answer
    B 14 seconds Correct Answer Incorrect Answer
    C 12 seconds Correct Answer Incorrect Answer
    D 15 seconds Correct Answer Incorrect Answer

    Solution

    Let the length and the speed of the train be 'x' metres and 'y' m/sec respectively.
    When it crosses the bridge,
    Or, {(x + 90) / y} = 9.................(I)
    When it crosses the pole,
    Or, (x / y) = 6
    So, x = 6y............(II)
    Or, 6y + 90 = 9y
    Or, 90 = 3y
    So, y = (90 / 3) = 30 m/sec
    And x = 30 × 6 = 180 metres
    So, relative speed of the train w.r.t. the van = 30 - 15 = 15 m/sec
    So, required time = (180 / 15) = 12 seconds

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