A man was walking through a tunnel. He is 1/4 of the way through when he hears a train approaching the tunnel from behind him.
If he turns and runs back, he will make it out of the tunnel just as the train is entering it (and will save himself by a hair). If he goes forward to the far end of the tunnel, he will also just barely make it, emerging from the tunnel just as the train is about to catch up to him.
If the man's running speed is 7 miles per hour, how fast is the train moving?
Good question levik. According to the question the terms in the second paragragh have not actually happened. As you can see you have started the para with "if", stating that the info given is conditional. When in the end you ask "how fast is the train moving?" logically it should mean the speed of the train even before it reaches the tunnel entrance. Since you have not stated any constancy in the train's speed before arrival to the tunnel entrance the speed of the train could be virtually anything.