Definition: 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.
Input: [9.477, 80.386, 229.39, 221.455, 172.89, 79.555, -7.837, 175.651, 147.418, 100.648]

120.903