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An airplane takes 7 hours to fly 2800 kilometers against the wind. The return trip with the wind takes only 4 hours. What is the speed, in kilometers per hour, of the airplane in still air?

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Answer: Let's call the speed of the airplane in still air "x".

Since the airplane takes 7 hours to fly 2800 kilometers against the wind, its speed against the wind is 2800/7 = 400 km/hr.

Since the return trip with the wind takes only 4 hours, the speed of the wind must be 400 - x.

The total speed of the airplane on the return trip is x + (400 - x) = 400 km/hr.

So, we have:

400 = x + (400 - x)

Expanding the right side:

400 = 400

Therefore, x = 400 km/hr, which is the speed of the airplane in still air.

Explanation:

User Szymon Pobiega
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