SOLUTION: 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?

Question 71572: 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) (Show Source): You can put this solution on YOUR website!
10=720/(X-30)+720/(X+30)
10=[720(X+30)+720(X-30)]/(X-30)(X+30)
10=[720X+21600+720X-21600]/(X^2-900)
10(X^2-900)=1440X
10X^2-1440X-9000=0
X^2-144-900=0
(X-150)(X+6)=0
X-150=0
X=150 ANSWER FOR THE SPEED OF THE PLANE IN STILL AIR.
THUS THE TWO SPEEDS FOR THE TWO TRIPS ARE
150-30=120 MPH & 150+30=180 MPH
PROOF
720/120+720/180=10
6+4=10
10=10
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