Warren is riding his bike at 15 mph on a road adjacent to railroad tracks. A train traveling at 90mph in the opposite direction as Warren, takes 20 seconds to pass him. How long is the train?
20 seconds is 1/180 hour
Assuming we can ignore the distance he travels in 20 seconds, since his speed is so much slower than the trains, we see that the train travels
15mi/hr * 1/180 hr = 15/180 mi = 1/12 mi = 440 ft