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: [155.467, -40.717, -24.529, -22.608, 38.752]
Example Output: 21.273

Example Input: [136.816, 121.886, 38.032, 81.322, -0.781, 112.95, 49.478, 219.21, -42.397]
Example Output: 79.613

Example Input: [178.931, 227.744, -94.385, 227.269, 27.205, -93.034, 243.507]
Example Output:
102.462