The student body of a large university consists of 60%f……

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

A.a probability function
B.a random variable
C.thee xpected value
D.random function

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

问答题在显著性水平α＝0.05时能否认为方案A和方案B在药品中转时间上存在差异？