Find the mean and variance for the data $6,7,10,12,13,4,8,12$

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$6,7,10,12,13,4,8,12$

Mean,    $\bar x = \frac{{\sum\limits_{i = 1}^8 {{x_i}} }}{n}$

$=\frac{6+7+10+12+13+4+8+12}{8}=\frac{72}{8}=9$

The following table is obtained

${x_i}$ $\left( {{x_i} - \bar x} \right)$ ${\left( {{x_i} - \bar x} \right)^2}$
$6$ $-3$ $9$
$7$ $-2$ $4$
$10$ $-1$ $1$
$12$ $3$ $9$
$13$ $4$ $16$
$4$ $-5$ $25$
$8$ $-1$ $1$
$12$ $3$ $9$
    $74$

Variance  $\left( {{\sigma ^2}} \right) = \frac{1}{n}\sum\limits_{i = 1}^8 {{{\left( {{x_i} - \bar x} \right)}^2} = \frac{1}{8} \times 74}  = 9.25$

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