SOLUTION: I cant seem to figuere out the answer to this question and was wondering if you guys can help me. Im not completely stumped but here is the question and here is how much i have.

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Question 636753: I cant seem to figuere out the answer to this question and was wondering if you guys can help me. Im not completely stumped but here is the question and here is how much i have.
A boat cruises 36mi against a 3mph current and 36 mi back in the direction of the same current. The round trip takes 5 hours what is the speed of the boat in still water?

speed of boat against stream x-3
speed of boat with stream x+3
however i think my equation is wrong.
I end up with something like this?
36/x-3 = 5 but im not sure what i should be doing about the other side of the equation.

Answer by ewatrrr(24785)   (Show Source): You can put this solution on YOUR website!
 

Hi,

Yes. speed of boat against stream x-3

Yes. speed of boat with stream x+3 

Note: D = rt  0r  

Question states*** The round trip takes 5 hours

 |Multiplying thru by (x-3)(x+3) so as all denominators = 1 

   36(x+3) + 36(x-3) = 5(x-3)(x+3)

         72x = 5(x^2 - 9)

        5x^2 - 72x - 45 = 0

factor: (5x + 3)(x -15) = 0 , 

             x = 15mph, speed of the boat in still water (throwing out negative solution for unit measure) 

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