Answer to POW #8:

At 6:00, Bill's watch says it is 6:10, so he thinks that it is 6:15. John's watch sys 5:50, so he thinks it's 5:40. Joe's watch says 5:55, so he thinks it's 5:45. Finally, Henry's watch says 6:05, so he thinks it is 6:15. This mean that at 6:00, when the train leaves, Bill and Henry are already at the station, but John and Joe are not. Therefore John and Joe miss the train.

Source: Mathematical Challenges, NCTM.