关于集合的一道题目，新东方的

心诚则灵的MM

If X and Y are sets of integers, X△Y denotes the set of integers that belong to set X or set Y, but not both. If X consists of 10 integers, Y consists of 18 integers, and 6 of the integers are in both X and Y, then X△Y consists of how many integers?

answer: 16

我本来做的是22， 因为我觉得X△Y=X+Y-XY=18+10-6=22，但是答案是（10-6）+（10-8）=16. WHY?

Thanks in advance for explainations.

心诚则灵的MM

段小q

因为是set X or set Y，lz你18+10的话就不是or的意思了啊

mingda99

全在X的：4个。 在X和Y的：6个。  全在Y的：12个     所以，X总共10个，Y总共18个，而 belong to set X or set Y, but not both=全在X+全在Y=16个