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！ 先谢谢啦
发表于 2011-10-23 10:31:34
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