And this is, we're getting to something called the raw score method. What we want to do is write this right here, just in terms of xi's. And then we really are at what you call the raw score method, which is oftentimes a faster way of calculating the variance. So let's see, what is mu equal to? What is the mean? The mean is just equal to the sum from i is equal to 1 to n of each of the terms. You just take the sum of each of the terms, and you divide by the number of terms there are.