Six months, a familys electric bills averaged $55 per month. the bills for the first five months were $57.60, 60, 53.25, 50.75, and 54.05. what was the electric bill in the sixth month

  $54.35

Step-by-step explanation:

The differences from the average value are ...

  2.60, 5.00, -1.75, -4.25, -0.95

The total of these differences is +0.65, so the final bill must have a value that is $0.65 lower than the average.

The bill for the 6th month is $54.35.

Check

The average of the bills for 6 months is ...

  (57.60 +60 +53.25 +50.75 +54.05 +54.35)/6 = 330/6 = 55