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: [153.723, 20.213, 185.644, 162.271, 132.806, 231.388, 157.011, -11.903, 171.249]

133.6