SOLUTION: This is a practical appliaction of quadratic equations. How would I set up the following solution to this problem? The hudson river flows at a rate of 3 miles per hour. A p

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: This is a practical appliaction of quadratic equations. How would I set up the following solution to this problem? The hudson river flows at a rate of 3 miles per hour. A p      Log On


   

Question 149794: This is a practical appliaction of quadratic equations.
How would I set up the following solution to this problem?

The hudson river flows at a rate of 3 miles per hour. A patrol boat travels 60 miles upriver, and returns in a total time of 9 hours. What is the speed of the boat in still water?


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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 __ time upstream plus time downstream equals 9 hr

upstream __ t=60/(r-3)

downstream __ t=60/(r+3)

[60/(r-3)]+[60/(r+3)]=9 __ multiplying by (r+3)(r-3) __ 60(r+3)+60(r-3)=9(r+3)(r-3)

120r=9r^2-81 __ 0=9r^2-120r-81 __ dividing by 3 __ 0=3r^2-40r-27