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: [247.927, -57.393, 107.266, 174.764, 72.691, 28.127, 189.231, -78.4, 91.335]

86.172