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: [83.565, 143.697, 5.891, 155.304, 78.853, 230.402, -3.872, 227.728, 169.259]

121.203