SOLUTION: A Plane flies 490 miles with the wind and 340 miles against the wind in the same length of time. If the speed of the wind is 30 mph, what is the speed of the plane in still air?
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Question 1016634: A Plane flies 490 miles with the wind and 340 miles against the wind in the same length of time. If the speed of the wind is 30 mph, what is the speed of the plane in still air? Answer by ikleyn(52794) (Show Source):
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A Plane flies 490 miles with the wind and 340 miles against the wind in the same length of time.
If the speed of the wind is 30 mph, what is the speed of the plane in still air?
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Let u be the speed of the plane in still air, in mph.
Then the speed of the airplane flying with the wind is u + 30, against the wind u - 30 mph relative to the Earth.
Your equation is
= .
To solve it, multiply both sides by (u-30)*(u+30).
490*(u-30) = 340*(u+30).
490u - 490*30 = 340u + 340*30,
490u - 340u = 340*30 + 490*30,
150u = (340 + 490)*30,
150u = 830*30
u = = 166 mph.
