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    Question

    An athlete running at three-quarters of her average speed

    takes 25 minutes extra than her usual time to finish a marathon. Find her usual time to finish the marathon.
    A 19 min Correct Answer Incorrect Answer
    B 12 min Correct Answer Incorrect Answer
    C 10 min Correct Answer Incorrect Answer
    D 25 min Correct Answer Incorrect Answer

    Solution

    ATQ,

    Let the usual speed of the athlete be '4s' km/h and the distance be 'd' km.

    Let the usual time taken be 't' hours.

    ATQ;

    (d/4s) = t

    Or, d = 4ts ........ (I)

    When she runs at three-quarters of her speed:

    (d/(3s)) = t + (25/60)

    Using equation (I), we have;

    (4ts/3s) = t + (5/12)

    Or, 4t = 3t + (5/12)

    Or, t = (5/12)

    Therefore, the usual time taken by the athlete to finish the marathon = (5/12) hours or 25 minutes.

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