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# 求算產品不合格比例

某產品的長度分配為平均數100 mm,標準差2 mm的常態分配,今銷售規格為 99 mm 加減5 mm,試求不合格的比例為何?

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- ?Lv 72 decades agoFavorite Answer
Z = (X-mean)/standard deviation

不及格為細於９４及大於１０４

細於９４的機率

Z = (94-100)/2

Z = -3

Area Z<-3 (by normal distribution table) 0.0013

大於１０４的機率

Z = (104-100)/2

Z = 2

Area Z>2 (by normal distribution table) 0.0228

不及格機率為0.0013 + 0.0228 = 0.0241

及格與不及格比 0.9759: 0.0241 = 約40.5 : 1

Source(s): 腦

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