NO.PZ2015120604000116
问题如下：
A population has a mean of 25 but its standard deviation is unknown. we select 100 members from the population to form a sample with a mean of 22.5 and a variance of 16. Calculate the standard error of the sample mean :
选项：
A.
0.04.
B.
0.2.
C.
0.40.
解释：
C is correct.
根据中心极限定理，样本均值是等于总体均值，题干中为何不相等？
