SOLUTION: Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 6-mph current, it took her 20 minutes longer to get there than to return. How fast will her bo

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Question 140681: Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 6-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water?
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
let x="speed in still water" __ d=rt __ t=d/r

upstream __ t+(1/3)=5/(x-6)

downstream __ t=5/(x+6)

substituting __ [5/(x+6)]+(1/3)=5/(x-6) __ multiplying by 3(x+6)(x-6)
__ 15(x-6)+(x+6)(x-6)=15(x+6)

15x-90+x^2-36=15x+90 __ x^2=216 __ x=sqrt(216)