You are walking across a rail bridge, and are 3/8 of the way across. You hear a train approaching behind you at 60 miles per hour. You do some quick calculation, and you realize that you can either run back or forward, and either way, you can make it to the end of the bridge and get off the tracks, just in time to avoid getting hit by the train. That is, you will get to the end of the bridge (either behind you or in front of you) the exact same time as the train. What is your running speed?
