The following table gives information on the amounts (in dollars) of electric bills for August 2012 for a sample of 50 families.
Amount of Electric Bill
(dollars) Number of Families
0 to less than 60............. 5
60 to less than 120........... 16
120 to less than 180........... 11
180 to less than 240.......... 10
240 to less than 300.......... 8
Find the mean, variance, and standard deviation. Give a brief interpretation of the values in the column labeled mf in your table of calculations. What does represent?