A weighted average of the value of a random variable, where the probability function provides weights is known as（）

单项选择题A sample of 400 observations will be taken from an infinite population. The population proportion equals 0.8. The probability that the sample proportion will be greater than 0.83 is（）

A.0.4332
B.0.9332
C.0.0668
D.0.5668

单项选择题From a population of 500 elements，a sample of 225 elements is selected.It is known that the variance of the population is 900.The standard error of the mean is approximately（）

A.1.1022
B.2
C.30
D.1.4847

单项选择题Given the following information：Standar ddeviation=8 Coefficient of variation=64% The mean would then be（）

A.12.5
B.8
C.0.64
D.1.25

单项选择题假设检验中拒绝域为（）

A.Z<-1.96
B.Z>1.96
C.Z>1.65
D.Z<-1.65

单项选择题一家电器销售公司的管理人员认为，每月的销售额是广告费用的函数，并想通过广告费用对月销售额作出估计。用电视广告费用作自变量，销售额作因变量进行回归分析。下表给出了相关的分析结果， 下列说法正确的是（）

A.广告费用每增加$1，000， 销售额增加$1.420 211
B.广告费用每增加$1，000， 销售额增加$1420. 211
C.广告费用每增加$1420.211， 销售额增加$1000
D.广告费用每增加$1， 销售额增加$363.689 1