A train leaves New York City for Alle City at 15 mph. At the very same time, a train leaves Alle City for New York City at 20 mph on the same track. At the same moment, a bird leaves the New York City train station and flies towards the Alle City train station at 25 mph. When the bird reaches the train from Alle City, it immediately reverses direction. It then continues to fly at the same speed towards the train from New York City, when it reverses its direction again, and so forth. The bird continues to do this until the trains collide. How far would the bird have travelled in the meantime ?