The following table gives the frequency distribution of the amounts of telephone bills for August 2012 for a sample of 50 families.
Amount of Telephone Bill
(dollars) Number of Families
40 to less than 70............ 9
70 to less than 100........... 11
100 to less than 130........... 16
130 to less than 160........... 10
160 to less than 190.......... 4
Calculate the mean, variance, and standard deviation