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: [30.7, 241.916, 245.677, -26.708, 212.446, 81.786, 208.412, 237.096, 155.359]
Example Output: 154.076

Example Input: [-7.892, -43.609, 46.236, -78.213, -76.066]
Example Output: -31.909

Example Input: [23.221, -50.559, 41.948, 136.19]
Example Output:
37.7