1. Four persons A,B,C and D are going to exchange gifts from one other. How many possible ways for exchanging so that all of them will not get back his/ her own gift?
2. 20 people are lining up in two rows. Each row consists of 10 people. How many different arrangements are possible? you many state your assumptions in answering this question.
Permutation and Combination
2008-02-13 10:30 pm
回答 (2)
2008-02-14 2:10 am
✔ 最佳答案
1.P(not get back own gift)=1-P(own gift)
=1-1/4
=3/4
2008-02-14 6:59 am
1) it is called circular permutation so the answer is (4-1)! = 3! = 3*2*1 = 6
2) 20! / 10!*10! = 184756
2) 20! / 10!*10! = 184756
參考: myself
收錄日期: 2021-04-13 15:08:07
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