The five observations $x,x+2,x+4,x+6$ and $x+8$ have mean 11. Find their variance.

Variance does not depend on $x$: deviations from the middle value are −4, −2, 0, 2, 4, so variance $=\frac{16+4+0+4+16}{5}=8$. (2.83 is the SD; the mean 11 is not needed.)