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    Question

    A train 420 metre long takes 21 sec to cross a man

    running at a speed of 3 km/hr in the direction same to that of train. What is the speed of the train?
    A 45 km/hr Correct Answer Incorrect Answer
    B 40 km/hr Correct Answer Incorrect Answer
    C 75 km/hr Correct Answer Incorrect Answer
    D 60 km/hr Correct Answer Incorrect Answer

    Solution

    Let the speed of the train be x Relative speed = (x - 3) km/hr ⇒ (x - 3) = (420 × 18)/(21 × 5) ⇒ (x - 3) = (7560)/(105) ⇒ x – 3 = 72 ⇒ x = 72 + 3 = 75 km/hr

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