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    Question

    Two trains ‘D’ and ‘E’ of lengths 660 metres and

    440 metres respectively are travelling towards each other. Ratio of speed of ‘D’ to ‘E’ is 3:2. If the trains take 55 seconds to cross each other from the time they meet, then find the average of speeds (in km/h) of trains ‘D’ and ‘E’.
    A 27 km/h Correct Answer Incorrect Answer
    B 31 km/h Correct Answer Incorrect Answer
    C 36 km/h Correct Answer Incorrect Answer
    D 45 km/h Correct Answer Incorrect Answer
    E 51 km/h Correct Answer Incorrect Answer

    Solution

    Let the speeds be 3y and 2y m/s respectively.
    Relative speed = 3y + 2y = 5y m/s
    ATQ,
    5y × 55 = 660 + 440
    ⇒ 275y = 1100
    ⇒ y = 4
    Therefore, required average = (3y + 2y) ÷ 2 = 2.5y
    = 2.5 × 4 = 10 m/s = 10 × (18/5) = 36 km/h

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