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: [91.753, 238.873, 173.636, 112.958, -4.835, 231.612, 242.081, 24.421, 71.62, 217.499]

139.962