A plane flies 500 miles with the wind and 300 miles against the wind in the same length of time. If the speed of the wind is 20 mph, what is the speed of the plane in still air?

Answer 1

R is the speed of the plane

(R+20) * t = 500

(R-20) * t = 300

Rt + 20t = 500

Rt - 20t = 300

2Rt = 800

Rt = 400

R = 400/t

[(400/t) + 20] * t = 500

400 + 20t = 500

20t = 500 - 400 = 100

t = 5 ---> R = 400/5 = 80

The speed of the plane is 80.

The speed of the wind is 20.

With the wind: (80+20)*5 = 100*5 = 500

Against the wind: (80-20)*5 = 60*5 = 300

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