Concept:
Standard deviation:
\[
\sigma = \sqrt{\frac{1}{n}\sum (x_i - \bar{x})^2}
\]
Step 1: Compute mean of data.
\[
\bar{x} = \frac{6+5+9+13+12+8+10}{7} = \frac{63}{7} = 9
\]
Step 2: Compute deviations from mean.
\[
6-9=-3,\ 5-9=-4,\ 9-9=0,\ 13-9=4,\ 12-9=3,\ 8-9=-1,\ 10-9=1
\]
Step 3: Square each deviation.
\[
9, 16, 0, 16, 9, 1, 1
\]
Step 4: Sum of squared deviations.
\[
9+16+0+16+9+1+1 = 52
\]
Step 5: Compute variance and standard deviation.
\[
\sigma = \sqrt{\frac{52}{7}} = \frac{\sqrt{52}}{\sqrt{7}} = \frac{\sqrt{53}}{7}
\]