2. 外语
  3. Select 3 people from 4 couples to form a group. Two people of one couple can not be selected at the same time. How many ways of

Select 3 people from 4 couples to form a group. Two people of one couple can not be selected at the same time. How many ways of

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问题 Select 3 people from 4 couples to form a group. Two people of one couple can not be selected at the same time. How many ways of selection are there?
选项 A、16
B、32
C、56
D、28
E、336
答案B
解析 我们分两步来做：
第一步：从4对人里面取出3对，共有方法C43；
第二步：从选出的3对人中，每一对里面选择1个人，共有方法C21×C21×C21。
利用乘法原理得到：C43×(C21)3=32，所以B为正确答案。
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