英语和数学都很好的进。。Toestimatethemeanageforapopulationof4000employees,asimplerandomsampleof40employeesisselected.Ifthepopulationstandarddeviationis8.2,computethestandarderrorofthesamplemean.Whatisthe

　　英语和数学都很好的进。。

　　Toestimatethemeanageforapopulationof4000employees,asimplerandomsampleof40employeesisselected.

　　Ifthepopulationstandarddeviationis8.2,computethestandarderrorofthesamplemean.

　　Whatistheprobabilitythatthesamplemeanageoftheemployeeswillbewithin±2yearsofthepopulationmeanage?

　　Amarketresearchfirmconductstelephonesurveyswitha40percenthistoricalresponserate.Whatistheprobabilitythatinanewsampleof400telephonenumbers,atleast150individualswillcooperateandrespondtothequestions?Inotherwords,whatistheprobabilitythatthesampleproportionwillbeatleast150/400=0.375?

　　这几道题怎么做。。。standarderror的公式是啥。。