A Sample of Charge Accounts at a Local Drug Store $\begin{array}{cc}\text { Unpaid Balance }&\text { Frequency }\\10-29 & 1 \\30-49 & 6 \\50-69 & 9 \\70-89 & 11 \\90-109 & 13\end{array}$

A sample of charge accounts at a local drug store revealed the following frequency distribution of unpaid balances.
$\begin{array}{cc}\text { Unpaid Balance }&\text { Frequency }\\10-29 & 1 \\30-49 & 6 \\50-69 & 9 \\70-89 & 11 \\90-109 & 13\end{array}$
a. Determine the mean unpaid balance.
b. Determine the variance.
c. Determine the standard deviation.
d. Compute the coefficient of variation.