Given the task definition and input, reply with output. 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.

[21.756, 126.526, 28.967, 186.044, 196.473, -40.251, -45.086, 17.535, 137.938, -91.651]

53.825