Two trains are 1 kilometer apart on a single track railway line. They set off towards one another at 1 m/second.
A bee sitting on the front of one of the trains sets off and starts to fly along the railway line at 3 m/second.
When the bee meets the other train it immediately turns around and flies towards the first train and so on . . .
How many times does the bee turn before the trains bump into each other?