A plane flies 465 miles with the wind and 315 miles against the wind in the same length of time. If the speed of the wind is 25 mph, find the speed of the plane in still air.

If the speed of the wind is 25 mph, then the plane's speed against the wind must be 415 mph, NOT 315 mph !!

[465 + 415] / 2 =440 mph - its speed in still air.

[465 - 415] / 2 =25 mph - the speed of the wind.

465(x-25) = 315(x+25)

150x = 19500

x = 130