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    Question

    A train of length (L + 90) meters crosses a man running

    in the same direction in 30 seconds. The same train crosses a bridge of length (L - 210) meters in 36 seconds. If the speed of the man is 18 kmph, then find the value of 'L'.
    A 480 Correct Answer Incorrect Answer
    B 510 Correct Answer Incorrect Answer
    C 540 Correct Answer Incorrect Answer
    D 570 Correct Answer Incorrect Answer
    E 600 Correct Answer Incorrect Answer

    Solution

    Let the speed of the train be 'S' m/s,

    Speed of the man = 18 kmph = 5 m/s

    Length of the train = (L + 90) metres

    ATQ,

    L + 90 = (S - 5) X 30

    L = 30S - 240 --- (i)

    Sum of the length of Train and bridge = L + 90 + L - 210

    = (2L - 120) metres

    Now,

    2L - 120 = 36S

    Using value of 'L' from equation (i), we get:

    2 X (30S - 240) - 120 = 36S

    Or, 60S - 480 - 120 = 36S

    Or, 24S = 600

    So, 'S' = 25

    Required value of 'L' = 30 X 25 - 240 = 510

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