Two trains start moving toward each other at the exact same time from tracks 200 miles apart. Train A travels at 40 mph, and Train B travels at 60 mph. At the same instant Train A starts, a remarkably fast housefly on Train A's front windshield begins flying toward Train B at 80 mph. When the fly hits Train B's windshield, it instantly turns around and flies back toward Train A at 80 mph, continuing this back-and-forth until the two trains collide. What is the total distance the fly traveled?
160 miles
Instead of calculating each leg of the fly's infinite bounces, find the total time the trains travel before colliding. Distance = 200 miles, closing speed = 40 + 60 = 100 mph. Time to collision = 200 / 100 = 2 hours. The fly travels at 80 mph for those exact 2 hours: 80 × 2 = 160 miles.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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