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Debbie traveled by boat 5miles upstream to fish in her favourite spot> Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water ????

Please help !!!!!!!!!!!!!!

  • MaTh -

    Let V be the speed in still water, in mph. The speed with respect to land will be V-4 upstream and V+4 downstream.

    Upstream travel time (in hours) = Downstream travel time + 1/3 hour.

    5/(V-5) - 5/(V+5) = 1/3

    Solve for V
    [5(V+5) - 5(V-5)]/(V^2 -25) = 1/3
    50/(V^2-25) = 1/3
    150 = V^2 -25
    V = sqrt 175 = 13.23 mph

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