In a message dated 99-07-28 17:59:56 EDT, you write: << A simple brain teaser: You are crossing a railroad bridge that spans a deep ravine. When you are 1/4 of the way across, you notice a train coming from behind. If you try to run across the rest of the bridge, the train will hit you just as you reach the other side. If you try to backtrack, the train will hit you at the very beginning of the bridge. Question: how fast is the train traveling relative to you? >> in relation to which of your speeds? the original walking speed? the running speed? or the standing there calculating where the trains going to hit you speed?