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.
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.
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发表于 2010-12-24 10:36:57
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