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

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

Example Input: [-94.475, 150.208, -46.949, 70.49, -4.341, -82.564, 144.79, 114.873, 2.76, 225.447]
Example Output:
48.024