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.
[217.523, 92.701, -55.65, -89.359, 55.742, 158.634, -31.883, 206.554]