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Math Help - Boat in Still Water

  1. #1
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    Boat in Still Water

    Debbie traveled by boat 5 miles upstream to fish in her favorite 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?
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  2. #2
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    Quote Originally Posted by magentarita View Post
    Debbie traveled by boat 5 miles upstream to fish in her favorite 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?
    Let the speed in still water be x mph
    When it travels upstream its speed= x-4 mph
    Time taken to go upstream= \frac{5}{x-4} h
    Speed in downstream = x+4 mph
    Time taken to go downstream or time taken to return back= \frac{5}{x+4} h
    And 20 min = \frac{20}{60}=\frac{1}{3} hrs
    But according to question...

    \frac{5}{x-4} -\frac{5}{x+4}=\frac{1}{3}

    Solve it and you will get the answer
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  3. #3
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    wow.....

    Quote Originally Posted by great_math View Post
    Let the speed in still water be x mph
    When it travels upstream its speed= x-4 mph
    Time taken to go upstream= \frac{5}{x-4} h
    Speed in downstream = x+4 mph
    Time taken to go downstream or time taken to return back= \frac{5}{x+4} h
    And 20 min = \frac{20}{60}=\frac{1}{3} hrs
    But according to question...

    \frac{5}{x-4} -\frac{5}{x+4}=\frac{1}{3}

    Solve it and you will get the answer
    You were able to come up with the right equation without creating a chart. Interesting.
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  4. #4
    Member great_math's Avatar
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    Quote Originally Posted by magentarita View Post
    You were able to come up with the right equation without creating a chart. Interesting.
    The only thing that is to be kept in mind while doing this question is that:

    when upstream subtract the speed of flow of water from the speed in still water and add when downstream
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  5. #5
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    ok..........

    Quote Originally Posted by great_math View Post
    The only thing that is to be kept in mind while doing this question is that:

    when upstream subtract the speed of flow of water from the speed in still water and add when downstream
    Thank you for the input.
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