An elderly guest at a hotel went out for a walk at 7:15 in the morning, ambling at a sedate two miles per hour. At 8:15 another guest went for a walk along the same path with his dog. He walked at a bit more active three miles per hour. The dog was full of beans and trotted off at five miles per hour.
The dog chased the first man along the path. When it reached him, it immediately turned around and ran back to its master. When it reached him, it turned right around and ran back to the first man, and kept this up - to and fro - right up until the second man caught up with the first man.
Are you able to calculate how far the dog ran altogether?