Two trains, each having a speed of 30 km/h, are headed at
each other on the same straight track. A bird that can fly 60 km/h
flies off the front of one train when they are 60 km apart and heads
directly for the other train. On reaching the other train, the bird
flies directly back to the first train, and so forth. (We have no idea
why a bird would behave in this way.) What is the total distance the
bird travels before the trains collide?