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: [192.278, 136.832, -19.412, 103.997, 244.988, 243.271, 129.71]

147.381