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: [139.238, 225.164, -21.563, -22.339, -77.136, 96.772, -40.208, 121.974, 228.852]
Example Output: 72.306

Example Input: [-66.735, 23.822, -34.5, 118.327, 242.333]
Example Output: 56.649

Example Input: [79.915, 123.829, -18.921, -7.76, 62.029, 66.334]
Example Output:
50.904