求助大家概率两个问题！
A box contains 12 connectors, 9 good and 3 defective. What is the probability of obtaining exactly 2 good and 1 defective connector in drawing 3 parts from the box without replacement?
答案应该是0.4909没什么问题。但是下面又是这个题的变形！不知道该怎么解了！求指点
A box contains 12 connectors, 9 good ones and 3 defective ones. What is the probability of obtaining exactly 2 good and 1 defective connector in drawing 3 parts from the box with replacement?
答案不是0.4909，应该是多少呀？
求指点啊！:mad: 先谢谢啦
答案应该是0.4909没什么问题。但是下面又是这个题的变形！不知道该怎么解了！求指点
A box contains 12 connectors, 9 good ones and 3 defective ones. What is the probability of obtaining exactly 2 good and 1 defective connector in drawing 3 parts from the box with replacement?
答案不是0.4909，应该是多少呀？
求指点啊！:mad: 先谢谢啦
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cliffnest (威望:9) (上海 ) 机械制造 经理 - Supplier quality managem...
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可放回抽样应该用二项分布？楼主找公式把。我的公式还给老师了。