What seems like a simple question about two trains hurtling towards each other, with a fly in between, actually fools most people. There's an easy way and a hard way of solving this and we run through both below.
Two trains, on the same track, are 200 miles apart and each is travelling at 50mph towards the other. Starting on one traine is a fly that can fly at 75mph, it flies from one train to the other and back again, until they collide. How far does the fly travel before the trains collide?