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: [206.49, 142.105, -86.289, 247.909, -67.045, 12.449, 64.45, 142.742, -18.657, 170.507]

81.466