下禮拜要考P...超緊張... 這邊有個SAMPLE中關於negative binominal的問題: 希望有大大幫忙解惑 A company takes out an insurance policy to cover accidents that occur at 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 is independent of the number of accidents that 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. 解答提供其中一個做法: 4! 5! 6! (2/5)^4 + -------*[(2/5)^4]*(3/5)+-------*[(2/5)^4]*(3/5)^2+-------*[(2/5)^4]*(3/5)^3=0.2898 3!*1! 3!*2! 3!*3! which can be derived directly or by regarding the problem as a negative binomial distribution with i) success taken as a month with no accidents ii) k = the number of failures before the fourth success, and iii) calculating Pr[k>=3] 我不是很懂為什麼要讓2/5每一項都要到四次方 想很久還是想不懂 麻煩大家了 感激不盡... --

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