Definition: 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.
Input: [-83.701, 71.935, 243.33, -69.743, 188.782, 158.333, 64.879, 147.785, -71.56, 218.262]

86.83