Question

A passenger plane and a jet leave at the same time from the same airport, traveling in opposite directions. The jet travels at twice the speed of the passenger plane. They are 420 miles apart after 4 hours. Find the speed of the jet.

Answer 1

Answer: 70 mph

Work Shown

x = speed of the passenger plane

2x = speed of the jet

distance = rate*time

d = r*t

d = x*4

d = 4x = distance the passenger plane travels at the 4 hour mark

d = 4(2x) = 8x = distance the jet travels at the 4 hour mark

The two distances add to 420 miles, as this is the gap between the airplanes at the 4 hour mark.

4x+8x = 420

12x = 420

x = 420/12

x = 35

So,

2x = 2*35 = 70 mph is the speed of the jet

This speed seems really low. Jet aircraft normally reach speeds between 400 mph and 600 mph.