Two trains 200 miles apart are moving toward each other; each one is going at a speed of 50 miles per hour. A fly starting on the front end of one of them flies back and forth between them at a rate of 75 miles an hour. It does this until the trains collide and crush the fly to death. What is the total distance the fly has flown?
Since the trains are 200 miles apart and each train is going at 50 miles an hour, it takes 2 hours for the trains to collide. Therefore the fly was flying for 2 hours. Since the fly was flying at the rate of 75 miles per hour, then the fly must have flown 150 miles.