A sample of 400 observations will be taken from an infi……

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？

问答题试求总体均值的置信水平为95%的置信区间。

问答题试求药品中转时间差异均值的点估计。