数学试题讲解

设

X_{1}, X_{2}, \dots, X_{n}

是来自总体

N (0, 1)

的简单随机样本, 记

\bar{X} = \frac{1}{n} \sum_{i = 1}^{n} X_{i}

, 则

D ({\bar{X}}^{2}) =

\frac{1}{n^{2}}

. B.

\frac{2}{n^{2}}

. C.

\frac{3}{n^{2}}

. D.

\frac{4}{n^{2}}