Eleven scientists are working on a secret project. They wish to lock up the documents in a cabinet such that the cabinet can be open if and only if six or more of scientists are present.What is the smallest number of keys to the locks each scientist must carry? 解答写要C(10,3)个keys 为什麽不是C(10,5)? 我的想法是 A必须持有任5位scientists所没有的key才能打开 而从10位scientist取5位有C(10,5)种取法 --

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