单选题 From a population of 5000 observations, a sample of n=100 is selected. Calculate the standard error of the sample mean if the population standard deviation is 50.

A、

A. 4.48.
B、

B. 5.00.
C、

C. 4.00.

【正确答案】 B

【答案解析】
The standard error of the sample mean equals the standard deviation of the population divided by the square root of the sample size: 50/(100)^1/2=5.