Hi, I am trying to use calculus to analyze the following puzzle. I already know the answer to the puzzle -200Km. What I want to be able to do is to model or calculate distance the fly travels in a particular sweep. See the attached Excel file to better understand what I mean. I feel that Calculus might help me in modeling the movement of the fly, but not sure. How should I go about doing this? Puzzle: Two trains are 200 km apart, and travelling towards each other at 100 km/hour each. From train A a fly takes off, flying straight above the rails to train B at the speed of 200km/hour, bounces off it and flies back to train A. This is repeated till the trains crash together and the fly is smashed. How much distance does the fly cover? Thanks.