SOLUTION: Sorry, but here's another word problem and i can barely do those that are already in equation form. The Hudson River flows at a rate of 3 miles per hour. A patrol boat travels 60

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: Sorry, but here's another word problem and i can barely do those that are already in equation form. The Hudson River flows at a rate of 3 miles per hour. A patrol boat travels 60       Log On


   

Question 144572: Sorry, but here's another word problem and i can barely do those that are already in equation form. 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?
Answer by checkley77(12844) About Me  (Show Source):
You can put this solution on YOUR website!
60/(x-3)+60/(x+3)=9
[60(x+3)+60(x-3)]/(x-3)(x+3)=9
(60x+180+60x-180)/(x^2-9)=9
120x=9x^2-81
9x^2-120x-81=0
Using the quadratic equation:x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+we get:
x=(120+-sqrt[-120^2-4*9*-81])/2*9
x=(120+-sqrt[14,400+2,916])/18
x=(120+-sqrt17,316)/18
x=(120+-131.59)/18
x=(120+131.59)/18
x=251.59/18
x=13.98 MPH for the speed of the boat.
proof
60/(13.98-3)+60/(13.98+3)=9
60/10.98+60/16.98=9
5.4645+3.5336=9
9~9