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: [164.406, 184.998, -66.442, 89.34, -1.556, -17.756, 247.809, -48.086, 146.561, 88.855]

78.813