[中學] 中學機率問題
徐式數學高一下3-3重點3說例4
有一棟三戶相連的住宅(假設由左到右依序為甲乙丙)
一年內每戶本身失火的機率為0.01,因鄰戶失火被波及的機率為0.2
試求各戶在一年內發生火災的機率
我的問題是:我用以下兩種算法算出兩個不同答案,兩個答案相差極小
可是我不知道其中的一個算法錯在哪裡,麻煩高手幫忙解答
以下是算"甲戶失火"的機率
法一(解答算法):
P(甲戶失火)
=1-P(甲戶沒起火 且 乙戶沒有"起火且傳給甲" 且 丙戶沒有"起火且傳給乙又傳給甲")
=1-P(甲戶沒起火)*P(乙戶沒有"起火且傳給甲")*P(丙戶沒有"起火且傳給乙又傳給甲")
=1-0.99 * [ 1-P(乙戶起火且傳給甲) ] * [ 1-P(丙戶起火且傳給乙又傳給甲) ]
=1-0.99 * [ 1-0.01*0.2 ] * [ 1-0.01*0.2*0.2 ]
=0.012375208
法二:
P(甲戶失火)
= P(甲戶起火) + P(甲戶沒起火但乙戶起火傳給甲)
+ P(甲戶和乙戶都沒起火但丙戶起火傳給乙又傳給甲)
=0.01 + 0.99*0.01*0.2 + 0.99*0.99*0.01*0.2*0.2
=0.01237204 (和解答的答案有微小差距)
謝謝各位
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05/11 22:51, , 1F
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看不懂你說的
※ 編輯: TrySoHard 來自: 220.131.203.219 (05/11 23:02)
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感覺不是耶,因為法二的答案比解答的小,所以應該是少算而不是重複算
而且法二裡面應該沒有把這種情況算兩次吧?
※ 編輯: TrySoHard 來自: 220.131.203.219 (05/12 00:35)
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