$1.(15$ points$)$ For a data sample of $17$ observations, we have

$17$

$$

i$=1$

xi $=34$ and

$17$

$$

i$=1$

x$2$i

$=468.$

Calculate:

$($a$)(5$ points$)$ the sample mean

$($b$)(5$ points$)$ the sample standard deviation

$($c$)(5$ points$)$ the coefficient of variation