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    Question

    Two trains ‘T4’ and ‘U4’ of lengths 360 metres and

    540 metres respectively are travelling towards each other. Ratio of speed of ‘T4’ to ‘U4’ is 2:3. If the trains take 36 seconds to cross each other from the time they meet, then find the average of speeds (in km/h) of trains ‘T4’ and ‘U4’.
    A 36 km/h Correct Answer Incorrect Answer
    B 40 km/h Correct Answer Incorrect Answer
    C 45 km/h Correct Answer Incorrect Answer
    D 54 km/h Correct Answer Incorrect Answer
    E 60 km/h Correct Answer Incorrect Answer

    Solution

    Let the speed of ‘T4’ and ‘U4’ be ‘2y’ and ‘3y’ m/s respectively.
    Relative speed = 2y + 3y = 5y m/s
    ATQ,
    5y × 36 = 360 + 540
    ⇒ 180y = 900
    ⇒ y = 5
    Therefore, required average = (2y + 3y) ÷ 2 = 2.5y
    = 2.5 × 5 = 12.5 m/s = 12.5 × (18/5) = 45 km/h

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