A plane flies 420 miles with the wind and 350 miles against

A plane flies 420 miles with the wind and 350 miles against the wind in the same length of time. If the speed of the wind is 15 mph, find the speed of the plane in still air.

Solution

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Let the speed of Plane in still air be x mph.

Given speed of wind = 15 mph

Speed of plane with the wind = x + 15

Speed of plane against the wind = x-15

Since the time taken in oth cases is same we can draw the equation

420/(x+15) = 350 / (x-15)

6/ (x+15) = 5/ (x-15)

6x - 90 = 5x + 75

x = 165 mph

Solution

Speed of plane in still air is 165 mph