(from Posner, 1973, Cognition: An introduction)
Two train stations are 50 miles apart. At 2pm one Saturday afternoon two trains start toward each other, one frm each station. Just as the trains pull out of the stations, a bird springs into the air in front of the first train and flies to the front of the second train. When it reaches the second train, it turns back and flies toward the first train. The bird continues to do this until the trains meet. If both trains travel at the rate of 25 miles per hour, and the bird flies at 100 miles per hour, how many miles will the bird have flown before the trains meet?