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.
[123.309, 136.445, -83.564, 50.477, 140.754, -53.693, 175.065, 191.215, 0.704]