SOLUTION: A plane flies 720 miles against a steady 30 mile per hour head wind and then returns to the same point with wind. If entire trip takes 10 hours, what is plane`s speed in still air?

Question 68691: A plane flies 720 miles against a steady 30 mile per hour head wind and then returns to the same point with wind. If entire trip takes 10 hours, what is plane`s speed in still air? I do not even know where to begin. Please help me. Thank you in advance.
Answer by checkley71(8403) (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)
10X^2-9000=1440X
10X^2-1440-9000=0
X^2-144-900=0
(X-150)(X+6)=0
X-150=0
X=150 ANSWER FOR THE PLANE'S SPEED IN STILL AIR.
PROOF
10=720/120+720/180
10=6+4
10=10

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