2. 外语
  3. If a couple give birth to only one child at a time and the probability of the child being male or female is the same, what is th

If a couple give birth to only one child at a time and the probability of the child being male or female is the same, what is th

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问题 If a couple give birth to only one child at a time and the probability of the child being male or female is the same, what is the probability of they having 2 boys and 2 girls?
选项 A、1/2
B、l/4
C、3/4
D、3/8
E、5/8
答案D
解析 题意是一对夫妇每次只生一个孩子，生男和生女的概率一样，问他们生下两男两女的概率?一共有多少种生法呢?生四个孩子，每次可男可女共两种情况，所以一共有24=16种可能。什么样的情况生两男两女呢?这种题目大家需注意，如果从四次中选择生两男的次数，那么剩下的两次必然全部生女，所以只要求出四次中生两男的情况，就等于是求出了生两男两女的情况，一共为C42=6种。所以所求概率为6/16=3/8，选择D。
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