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: [217.978, 70.977, 31.129, -87.408, -99.013, 249.862, -87.151, 207.527, 43.432]
Example Output: 60.815

Example Input: [231.74, 142.135, 60.231, -34.154, 111.503, -84.615, 186.711, 52.235, 43.888, -20.096]
Example Output: 68.958

Example Input: [85.925, 218.341, -55.232, 136.11, 243.387, 98.158, 183.742, 85.875, 124.291, -95.213]
Example Output:
102.538