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.
[226.982, 80.482, 220.959, -70.455, -34.905, -53.787, 218.616, 70.433, -53.24]