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    Question

    A runner, going at five-sixths of her normal speed, takes

    10 minutes longer than usual to complete a race. What is her usual time?
    A 19 min Correct Answer Incorrect Answer
    B 12 min Correct Answer Incorrect Answer
    C 10 min Correct Answer Incorrect Answer
    D 27 min Correct Answer Incorrect Answer

    Solution

    ATQ,

    Let the usual speed of the runner be '6s' km/h and the distance be 'd' km.

    Let the usual time taken be 't' hours.

    ATQ;

    (d/6s) = t

    Or, d = 6ts ........ (I)

    Now, running at five-sixths of her speed:

    (d/(5s)) = t + (10/60)

    Using equation (I), we have;

    (6ts/5s) = t + (1/6)

    Or, 6t = 5t + (1/6)

    Or, t = (1/6)

    Thus, the usual time taken by the runner to complete the race = (1/6) hours or 10 minutes.

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