抽樣分配一題~~ - 考試
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By Isabella
at 2013-05-29T19:53
at 2013-05-29T19:53
Table of Contents
廠商宣稱燈泡壽命成常態分佈,平均壽命100天,標準差25,於10月1日當天裝設3000個燈
泡,試問,
(1)12月結束時,預計應更換幾個燈泡呢?
(2)12月結束時,更換900個燈泡以上的機率呢?
原本以為只是很單純的題目,但是就是解不出來~"~
u~N(100,25^2)
X~N(100,25^2/3000)
到12月底共91天
第一題我理解為求"壽命小於91天的燈泡機率"
P(u<91)=P(Z<-19.71)
好吧,我應該是算錯了,這Z值好詭異....
第二小題是用樣本比例的概念去解嗎?
連式子都不知該怎麼列...
請問問題出在哪呢?
--
泡,試問,
(1)12月結束時,預計應更換幾個燈泡呢?
(2)12月結束時,更換900個燈泡以上的機率呢?
原本以為只是很單純的題目,但是就是解不出來~"~
u~N(100,25^2)
X~N(100,25^2/3000)
到12月底共91天
第一題我理解為求"壽命小於91天的燈泡機率"
P(u<91)=P(Z<-19.71)
好吧,我應該是算錯了,這Z值好詭異....
第二小題是用樣本比例的概念去解嗎?
連式子都不知該怎麼列...
請問問題出在哪呢?
--
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考試
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