2006-II-54

$\begin{array}{cl}
= & \dfrac{10a+1 + 10a+3 + \ldots + 10a + 9}{5} \\
= & 10a + 5
\end{array}$

該五個數字的標準差

$\begin{array}{cl}
= & \sqrt{\dfrac{(10a+1 -(10a+5))^2 + \ldots + (10a+9 -(10a+5))^2}{5}} \\
= & \sqrt{\dfrac{40}{5}} \\
= & \sqrt{8} \\
= & 2\sqrt{2}
\end{array}$