x! refers to a factorial of x. Meaning, that if x = 5, then x! = 5*4*3*2*1 = 120. In Python we can use the scipy library:

from scipy.special import factorial
> 120

X bar is a reference to the sample mean (as opposed to the population mean.)

In Python you can calculate a mean quite quickly with Numpy:

import numpy as np
>> 16


μ (pronounced “mu” or “mew”) is the Greek letter used to reference the population mean.


A Greek Sigma of course means the SUM over a set.

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