Systems of linear equations: distance, rate and time
Two Trains
A freight train leaves at 40 mph; an express follows two hours later at 60 mph. A three-minute film on why the catch-up is the crossing of two lines, and why a graph is just the story seen from above.
This browser has 3D graphics turned off, so the set cannot be drawn. The math and the narration still play.
The problem
A freight train leaves a station heading east at 40 miles per hour. Two hours later an express train leaves the same station on a parallel track heading east at 60 miles per hour. How many hours after the express leaves does it catch the freight train?
4 hours
