Question 50117
A plane flies 720 mi against a steady 30-mi/h head wind 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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With the wind DATA:
distance = 720 mi ; rate = p+30 mph ; time = d/r= 720/(p+30)
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Against the wind DATA:
distance = 720 mi ; rate = p-30 mph ; time = d/r = 720/(p-30)
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EQUATION:
time + time = 10 hrs.
720/(p+30) + 720/(p-30)= 10
72/(p+30) + 72/(p-30)= 1
72p+72p = p^2-900
p^2-144p-900=0
(p-150)(p+6)=0
plane speed = 150 mph
cheers,
Stan H.