问一道英文数学题目（美国高中水平的）

题目

问一道英文数学题目（美国高中水平的）
In a survey of 63 people,23 people subscribed to magazine A,21 people subscribed to magazine B,and 17 subscribed to magazine C.For any two of the magazaines,4 people subscribed to both magazines but not to the thrid magazine.If 5 people in the survey did not subscribe to any of three magazines,how many people subscribed to all three magazines?
怎么我一直做都是负数呢?

答案

这道题很奇怪啊.
条件1：For any two of the magazaines,4 people subscribed to both magazines but not to the thrid magazine,
说明,有三组四个人的同时订了两个杂志,这个时候投票名额就用了24票.
也就是说,12个人,24票.
条件2：If 5 people in the survey did not subscribe to any of three magazines
也就是说,5个人,0票.
这个时候总共63个人,减掉就只剩下46个人.
总共三组投票投了23+21+17=61票.
减掉就剩下37票.
最多一人投一个magazine,这时候还有9个人没有票投!
好random.难怪是负的.