21. 某工厂生产某种电子产品,每件产品不合格的概率均为
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3Ep%3C%2Fmi%3E%3C%2Fmath%3E)
,现工厂为提高产品声誉,要求在交付用户前每件产品都通过合格检验,已知该工厂的检验仪器一次最多可检验
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmn%3E5%3C%2Fmn%3E%3C%2Fmath%3E)
件该产品,且每 件产品检验合格与否相互独立.若每件产品均检验一次,所需检验费用较多,该工厂提出以下检 验方案:将产品每
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3Ek%3C%2Fmi%3E%3C%2Fmath%3E)
个
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmrow%3E%3Cmo%3E%28%3C%2Fmo%3E%3Cmrow%3E%3Cmi%3Ek%3C%2Fmi%3E%3Cmo%3E%E2%89%A4%3C%2Fmo%3E%3Cmn%3E5%3C%2Fmn%3E%3C%2Fmrow%3E%3Cmo%3E%29%3C%2Fmo%3E%3C%2Fmrow%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
一组进行分组检验,如果某一组产品检验合格,则说明该组内产品均合格,若检验不合格,则说明该组内有不合格产品,再对该组内每一件产品单独进行检验,如此,每一组产品只需检验1次或
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmn%3E1%3C%2Fmn%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmi%3Ek%3C%2Fmi%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
次.设该工厂生产1000件该产品,记每件产品的平均检验次 数为X.