Question 741947
If a plane can travel 500 miles per hour with the wind  and 420 miles per hour against the wind, what is the speed of the plane in still air?
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Equations:
p + w = 500 mph
p - w = 420 mph
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Add and solve for "p":
2p = 920
plane speed = 460 mph
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Solve for "w":
p + w = 500
460 + w = 500
wind speed = 40 mph
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Cheers,
Stan H.