SOLUTION: Science and medicine. A plane flies 720 mi against a steady 30-mi/h headwind and then returns to the same point with the wind. If the entire trip takes 10 h, what is the plane’s s

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Question 77740: Science and medicine. A plane flies 720 mi against a steady 30-mi/h headwind
and then returns to the same point with the wind. If the entire trip takes 10 h, what is the plane’s speed in still air?
Answer by checkley75(3666) About Me  (Show Source):
You can put this solution on YOUR website!
720/(x-30)+720/(x+30)=10
(720[x+30]+720[x-30])/(x-30)(x+30)=10
10(x^2-900)=720x+21600+720x-21600
10x^2-9000=1440x
10x^2-1440x-9000=0
x^2-144x-900=0
(x-150)(x+6)=0
x-150=0
x=150 answer for ther plane's speed in still air.
proof
720/120+720/180=10
6+4=10