扫描二维码，直接登录
题库 / OG2017Q-PS-168
A couple decides to have 4 children. If they succeed in having 4 children and each child is equally likely to be a boy or a girl, what is the probability that they will have exactly 2 girls and 2 boys?
~$3 \over 8$~
~$1 \over 4$~
~$3 \over 16$~
~$1 \over 8$~
~$1 \over 16$~
还没有题目讲解（毕出老师会陆续发布对官方考题的解读，请保持关注）。
So here we have four positions and there are two options to fill each position
so total number of cases=2x2x2x2=16
now we need 2boys and 2 girls OR we can say that we simply need 2 boys because if its not a boy it has to be a girl
favourable cases=4C2=6
probability=6/16=3/8
登录 或 注册 后可以参加讨论