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    Question

    A train of length (Q + 30) metres passes a pole in 18

    seconds and a tunnel of length 540 metres in 36 seconds. Find the time (in seconds) the train will take to cross a bridge of length '2Q' metres.
    A 33 secs Correct Answer Incorrect Answer
    B 45 secs Correct Answer Incorrect Answer
    C 52 secs Correct Answer Incorrect Answer
    D 25 secs Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ,

    Speed of train = [(Q + 30) ÷ 18] m/s

    Also, speed = [(Q + 30 + 540) ÷ 36]

    So, [(Q + 30) ÷ 18] = [(Q + 570) ÷ 36]

    Or, [(Q + 30) ÷ 1] = [(Q + 570) ÷ 2]

    Or, 2 × (Q + 30) = Q + 570

    Or, 2Q + 60 = Q + 570

    Or, Q = 510

    Speed = [(510 + 30) ÷ 18] = 540 ÷ 18 = 30 m/s

    Length of train = Q + 30 = 540 metres

    Required time = (540 + 2 × 510) ÷ 30 = 1560 ÷ 30 = 52 seconds

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