Question 1138664
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The "time" equation is


    {{{4/(10+c)}}} + {{{4/(10-c)}}} = {{{5/6}}}   of an hour.


    4*6*(10-c) + 4*6*(10+c) = 5*(10+c)*(10-c)

    240 - 24c + 240 + 24c   = 5*(100-c^2)

     480                    = 500 - 5c^2

     5c^2 = 500 - 480

     5c^2 = 20

     c^2   = 20/5 = 4

     c = {{{sqrt(4)}}} = 2.


<U>ANSWER</U>.  The speed of the current is 2 miles per hour.
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Solved.