An airplane flies 700 miles with a tail wind in 2.0 hrs. If it takes 2.5 hrs to cover the same distance against the headwind, then what is the speed of the plane in still air? A).290mph B).315mph C).240mph D).330mph E).250mph

B).315mph

Explanation:

Let the speed of the plane = p

Let the speed of the wind = w

Set up the system equation as;

                                     Relative V:               Time:                          Distance:

in wind direction:          p + w                         2                                  700

against wind:                 p - w                         2.5                                700

2(p + w) = 700

2.5(p - w) = 700

2p + 2w = 700

2.5p - 2.5w = 700

2.5  x:     5p + 5w = 1750

2  x:        5p - 5w = 1400

10p = 3150

p = 315 mph

Therefore, he speed of the plane in still air is 315 mph