SOLUTION: An 8-man rowing crew rows at a speed of 10 miles per hour in still water. every morning they practice bt rowing 4 miles upstream and then 4 miles downstream. If it takes them 5/6 o

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Question 1138664: An 8-man rowing crew rows at a speed of 10 miles per hour in still water. every morning they practice bt rowing 4 miles upstream and then 4 miles downstream. If it takes them 5/6 of an hour to complete the trip what is the speed of the current?
Answer by ikleyn(52805) About Me  (Show Source):
You can put this solution on YOUR website!
.
The "time" equation is


    4%2F%2810%2Bc%29 + 4%2F%2810-c%29 = 5%2F6   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%284%29 = 2.


ANSWER.  The speed of the current is 2 miles per hour.

Solved.