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: [80.285, 75.631, 5.715, -68.695, 134.225, 22.744, 63.203, 136.862, 60.995]
Example Output: 56.774

Example Input: [-90.211, -60.08, 99.87, 18.704, 197.269, 173.722, 168.875]
Example Output: 72.593

Example Input: [74.423, 9.21, 186.401, 131.036, -59.984]
Example Output:
68.217