Essentials of Statistics (5th Edition)

The mean can be counted by summing all the data and dividing it by the number of data: $\frac{3+6.5+6+5.5+20.5+7.5+12+20.5+11.5+17.5}{10}=11.05$: $\mu=11.05$ Variance=$\frac{\sum (x-\mu)^2}{n}=\frac{(3-11.05)^2+(6.5-11.05)^2+...+(17.5-11.05)^2}{5}=41.75.$ Standard deviation=$\sqrt{variance}=\sqrt{41.75}=6.46$ Range=maximum value-minimum value=$20.5-3=17.5$.