Cell Phone Calls
the Frequency of Cell Phone Call Per

Cell phone calls
The frequency of cell phone call per day on a certain account is tabulated in the following table:
$$\begin{array} { | c | c | } \hline \text { Calls per Day } & \text { Number af Days } \\\hline 0 - 2 & 12 \\\hline 3 - 5 & 8 \\\hline 6 - 8 & 5 \\\hline 9 - 11 & 3 \\\hline 12 - 14 & 1 \\\hline 15 - 17 & 1 \\\hline\end{array}$$
-Calculate the standard deviation of calls per day.