Distance/speed/time question. Can someone please walk me threw it?

Question

A 1-mile long train traveling at 1 mile per minute passes through a 1 mile long tunnel. How much time does it take the train to pass completely through?

Step-by-step please. =]

Answer 1

2 minutes

The train starts at the opening of the tunnel.  It takes 1 minute for the train to fill the tunnel. ( the front of the train to get from the opening to the end. It takes an additional minute for the train to clear the tunnel.