Part A
The formula for calcuating mean is expressed as
mean = sum of terms/number of terms
In this scenario,
mean = sum of bills/number of bills
From the information for family C in the table
Sum of bills = 134.51 + 118.06 + 109.28 + 90.15 + 91.20 + 96.36 + 130.71 + 129.16 + 107.77 + 100.95 + 107.64 + 123.82 = 1339.61
number of bills = 12
Mean = 1339.61/12
mean = 111.63
The mean of the electric bills for family C is $111.63
Part B
For company A,
Sum of bills = 88.82 + 84.8 + 62.35 + 65.17 + 60.2 + 74.86 + 92.15 + 99.89 + 96.45 + 81.63 + 64.12 + 72.18 = 943.02
number of bills = 12
Mean 943.02/12 = 78.59
The formula for calculating the mean absolute deviation is expressed as
MAD = ΣIx - meanI/n
MAD = [I88.82 - 78.59I + I84.8 - 78.59I + I62.35 - 78.59I + I65.17 - 78.59I + I60.2 - 78.59I + I74.86 - 78.59I + I92.15 - 78.59I + I99.89 - 78.59I + I96.45 - 78.59I + I81.63 - 78.59I + I64.12 - 78.59I + I72.18 - 78.59I]/12
Mean absolute deviation = 12.07
Part C
Mean absolute deviation = vi