In this task you will be given a list of numbers and you need to find the mean (average) of that list. The mean of a list can be found by summing every number in the list then dividing the result by the size of that list. The output should be rounded to 3 decimal places.
[205.331, 212.917, 143.657, 235.033, -83.9, 54.057, 88.002, 20.22]