A sample of charge accounts at a local drug store revealed the following frequency distribution of unpaid balances:
$10-$29 frequency(5)
$30-$49 frequency(10)
$50-$69 frequency(6)
$70-$89 frequency(9)
$90-$109 frequency(20)
What is the mean unpaid balance (2 decimals), standard deviation (2 decimals), and coefficient of variation (2 decimals)?