So that just becomes the sum from i is equal to 1 to n times x sub i squared divided by big N. Now, this is interesting. What is, if I take each of the terms in my population and I add them up and then I divide it by n, what is that? This thing right here. If I sum up all the terms in my population and divide by the number of terms there are. That's the mean, right? That's the mean of my population. So this thing right here is also mu.