(Moving Sets --- Three Sets)
For a company to hire a new employee, it must receive three references (recommendation
letters) from three interviewers. There are 15 applicants who got a reference from the
first interviewer; there are 17 applicants who got a reference from the second interviewer;
there are 20 applicants who got a reference from the third interviewer. The total number
of applicants is 30. What is the least possible number of applicants who could be hired?
Answer Choices: 0, 2, 3, 10 …
答案：E