题目内容：

Bill,George,Sally and Ann are brothers and sisters ,One of them is 15,one is 12.One of the boys is 13,and one of the girls is 14,Bill is older than Sally but Ann isn't.How old are they?
Bill is George is Sally is Ann is

优质解答

Bill 15 George 13 Sally 14 Ann 12
已知他们本别是15、14、13、12岁.
Bill、George中必有一个是13岁,Sally、 Ann 中必有一个是14岁（One of the boys is 13,and one of the girls is 14）.
Bill比Sally大,Sally比Ann大（Bill is older than Sally but Ann isn't）
根据“Sally、 Ann 中必有一个是14岁”的条件,假设Ann是14岁,由于Sally比Ann大,那么Sally只能是15岁.由于Bill比Sally大,那么Bill的岁数大于15,不符合12、13、14、15岁的条件.所以无解.
又假设Sally是14岁,由于Bill比Sally大,所以Bill只能是15岁,那么George就是13岁.Ann12岁,也满足"Sally的岁数大于等于Ann的岁数"的条件.
当然,你也可以根据BOYS的年龄条件作假设求解.答案是一样的.