A plane flies 425 miles with the wind and 350 miles against the wind in the same length of time.

Question

If the speed of the wind is 15 mph, find the speed of the plane in still air.

Answer 1

distance = rate * time

425 = (r+15)* t = rt + 15t

350 = (r-15)*t = rt - 15t

775 = 2rt

387.5 = rt

Substitutes:

425 = 387.5 + 15t

350 = 387.5 - 15t

Solves:

37.5 = 15t

=37.5 = -15t

SO t = 2.5

Substitutes again:

425 = (r + 15)* 2.5

4250 = 25(r+15) <--- multiplies by 10

170 = r + 15

r = 155

The speed of the plane is 155 mph

With the wind, 2.5 ( 155+15) = 2.5 * 170 = 425

Against the wind 2.5( 155-15) = 2.5*140 = 350

The speed of the plane is 155 mph