Two trains travel toward each other on the same track, beginning 100 miles apart. One train travels at 40 mph (miles per hour); the other travels at 60 mph.
A fly starts flight at the same location as the faster train, flying at a speed of 90 mph. When it reaches the slower train, it turns around, flying the other direction at the same speed. When it reaches the faster train again, it turns around, and so on. When the trains meet, how far will the fly have flown?
The fly would have travelled 90 miles.
The trains are 100 miles apart, and the trains are travelling toward each other at 40 and 60 mph, the trains will meet in one hour. The fly will have been flying for an hour at 90 mph at that point, so the fly will have travelled 90 miles.