Question: A family's water and electricity bills average $30 a month for the first 4 months and $24 a month for the last 2 months. If the family's bills were averaged over all 6 months, what would the average monthly bill be? Think carefully first, then make a decision:
The sum of the bills of the family in the first 4 months is $30 / month x 4 months = $120. The sum of the bills of the family in the last 2 months is $24 / month x $2 = $48. The sum of the bills of the family over the 6 months is $120 + $48 = $168. Hence, their average monthly bill is $168 / 6 months = $28 / month. So the answer is 28.