Prep T2-DS-12

[w062611]

Sets A, B, and C have some elements in common. If 16 elements are in both A and B, 17 elements are in both A and C, and 18 elements are in both B and C, how many elements do all three of the sets A, B, and C have in common?

(1) Of the 16 elements that are in both A and B, 9 elements are also in C.

(2) A has 25 elements, B has 30 elements, and C has 35 elements.

答案為 A

我選了B

拜託高手指導一下

A 也不太懂意思為何

感謝了

[hwatai]

題目問ABC的交集為何？

(A) AB交集為為16個，而其中有9個也是C的element，直接說明了ABC交集為9

(B) 由於A+B+C-AB交集-BC交集-AC交集+ABC交集=ABC聯集
由(B)可得25+30+35-16-17-18+ACB交集=ABC聯集
還少了一個條件，不充份