2001年的一道真题 A company takes out an insurance policy to cover accidents that occurat its manufacturing plant. The probability that one or more accidents will occur during any given month is 3/5 . The number of accidents that occur in any given month 5 is independent of the number of accidentsthat occur in all other months. Calculate the probability that there will be at least four months in which no accidents occur before the fourth month in which at least one accident occurs. 请问这道题的问题究竟该怎么理解啊，我越看越乱。。。。。。真心求助啊！！谢谢大家了！！
eddiechen 发表于 2012-5-16 01:12
This is SoA sample problem #43. Have you checked the solution?
http://www.soa.org/files/pdf/edu-200 ...
就是不明白为什么k = the number of failures before the fourth success。。。。。为什么是4.。。。题目最后一句话我和另一个同学都没读明白。。。所以想为什么是until 4 successes，，，这道题的问题是不是：计算至少四个月的情况下，前三个月没有发生事故并且第四个月发生至少一次事故的概率？
因为对负二项分布实在不熟悉，所以还请帮忙解答一下啊。。。这么晚了因为这个都睡不着觉。。。闹心。。
这个题目是问得有点模棱两可，你理解题目问题错了。
我们把一个月至少有一个accident看作success，这里是问＂在得到第四个success前至少有间隔四个月其中都没有accident，之前已经有3个success。＂换句话说我们要求＂at least four failures occur before the fourth success.＂
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