问题
单项选择题
An analyst gathered the following information about a stock index: Mean net income for all companies in the index $ 3.2 million Standard deviation of net income for all companies in the index-$ 4.8 million If the analyst takes a sample of 36 companies from the index, the standard error of the sample mean is closest to:（）
A. $ 66667.
B. $ 88889.
C. $ 800000.
答案
参考答案：C
解析：
The standard error of the sample mean is equal to the population standard deviation divided by the square root of the number of observations in the sample:$ 4800000/436=$800000.