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    Question

    Train 'M' can cross a pole in 10 seconds and a 200 metres

    long bridge in 15 seconds. Train 'N' whose length is 50% of the length of train 'M' runs in the same direction of train 'M'. If train 'N' crosses train 'M' in 15 seconds, then find the speed of train 'N'.
    A 72 m/s Correct Answer Incorrect Answer
    B 76 m/s Correct Answer Incorrect Answer
    C 80 m/s Correct Answer Incorrect Answer
    D 84 m/s Correct Answer Incorrect Answer
    E 88 m/s Correct Answer Incorrect Answer

    Solution

    Let the length and the speed of the train 'M' be 'x' metres and 's' m/s.
    ATQ,
    (x/s) = 10
    So, 'x' = 10s.........(i)
    Also, {(x + 200) ÷ s} = 15
    Or, 10s + 200 = 15s [from equation (i)]
    Or, 200 = (15s - 10s)
    Or, 's' = (200/5) = 40
    Length of train 'M' = (10 × 40) = 400 metres
    So, length of train 'N' = (400 × 0.50) = 200 metres
    Let the speed of train 'N' be 'n' m/s.
    ATQ,
    (400 + 200) ÷ (n - 40) = 15
    Or, 600 = 15 × (n - 40)
    Or, (n - 40) = 40
    So, 'n' = 40 + 40 = 80
    Therefore, speed of train 'N' = 80 m/s

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