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?
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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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