<PRE><B>Question 406189</B>
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Hi
speed of the current is 2 mph
Let (x+2mph) and (x-2mph) represent the speed of the boat down and upstream respectively,
D = r*t  OR t = D/r
Question states*** (total time up and down is 6 hr)
 5/(x+2) + 5/(x-2) = 6  |multiplying thru by (x+2)(x-2)
5(x+2) + 5(x-2)=6(x+2)(x-2)
 10x = 6(x^2 - 4)
   6x^2 -10x - 24 = 0
  2(3x^2 -5x - 12) = 0
   (3x^2 -5x - 12)= 0
factoring
   (3x +4)(x-3)= 0 Note:SUM of the inner product(4x) and the outer product(-9x) = -5x
   (3x +4)= 0 |tossing out negative solution for speed
     (x-3)= 0  x = 3mph, speed of boat in still water

CHECKING our Answer***
   5/5 + 5/1 = 6hr</PRE>