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: [-61.921, -27.056, 49.121, -13.842, -24.863, -16.545, 64.789, 61.42, 249.595, -96.877]

18.382