2 rhinos are charging towards each other from a distance of 100 metres apart. They are travelling at 5 metres per second. A fly starts from the horn of one of the rhinos and flies directly to the horn of the other rhino at a speed of 12 metres per second. When it arrives it immediately turns and flies back to the horn of the other rhino and repeats this behaviour until the 2 rhinos collide.

How far does the fly travel during this time?
An efficient, elegant method is required to solve this problem