Five numbers 1, 2, 3, 4, 5. The total combination of these 5 numbers is A55. Among them, 1, 2, and 3 are indistinguishable in the sense that 1, 2, and 3 are exchangable. Therefore, A33 combinations correspond to one unique arrangement. Thus, the answer is A55/A33.作者: sdcar2010 时间: 2010-12-24 11:28
60%的人参加了A项目，75%的人参加了B项目，问两个项目都参加的人数占总人数的百分比
I guess it asks for AT LEAST what percentage of people attend both project. To get the smallest possible number of people who are in both projects, for those 40% people who are not in project A, we put them in project B. Then at least 35% of people are in both B and A.