Two cyclists start cycling towards each other with an even speed of 10km/h. They start of 20km away from each other. At the same time a fly starts from one of them and flies to the other one, back to the first, and so on until they meet. How far has the fly flown in the end if it flew with a speed of 15km/h? I'm thinking it has to be 15km, since the two guys will meet half way after 1 hour, and the fly flies 15km in one hour. Can someone confirm this?