Answer
See below.
Work Step by Step
The mean of $n$ numbers is the sum of the numbers divided by $n$. The median of $n$ is the middle number of the numbers when they are in order (and the mean of the middle $2$ numbers if $n$ is even). The mode of $n$ numbers is the number or numbers that appear(s) most frequently. Hence here the mean: $\frac{5+5+7+8+9+11+11+15}{8}=8.875$, the median is the mean of the middle items in the sequence $5, 5, 7, 8, 9, 11, 11, 15 $, which is: $(8+9)/2=8.5$, the mode is $5,11$. The range is the difference between the largest and the smallest data value. The standard deviation of $x_1,x_2,...,x_n$ is (where $\overline{x}$ is the mean of the data values): $\sqrt{\frac{(x_1-\overline{x})^2+(x_2-\overline{x})^2+...+(x_n-\overline{x})^2}{n}}$. Hence here the range is: $15-5=10$ and the standard deviation is: $\sqrt{\frac{(5-8.875)^2+(5-8.875)^2+...+(15-8.875)^2}{8-1}}\approx3.1795$
