SOLUTION: an airplane took 2 hours to fly 600km against a head wind. the return trip with the wind took 1 2/3 hours. find the speed of the plain in still air.

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Let plane speed in still air = p
Let wind speed = w

Against the wind, the plane speed is p-w and time = 2 hours
With the wind, the plane speed is p+w and time = 1 hr 40 min. Distance = 600km for both flights.

OK...definitions over, now the solution.

Speed = distance/time

against the wind: (p-w) = 600/2 --> p-w = 300
with the wind: (p+w) = --> p+w = 360

Since we are asked for the plane's speed in still air (ie p, from the definition), we will add the 2 equations together to give 2p = 660.
So, p = 660/2
--> p = 330km/hr

jon.