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.

Example Input: [15.293, 221.056, 241.387, 81.3, 102.644, 146.885, -33.65, -36.56, -69.176]
Example Output: 74.353

Example Input: [24.119, 239.006, 239.873, 236.27, 134.34]
Example Output: 174.722

Example Input: [-12.951, -86.706, 228.633, -86.97, 212.037, 68.463]
Example Output:
53.751