So just playing with a little algebra we got from this thing, where you have to, each time, take each of your data points, subtract the mean from it, and then square it. And then, of course, before you had to do anything, you had to calculate the mean. And you take the square, then you sum it all up, then you take the average, essentially, when you divide it, when you sum and divide it by n. We've simplified it, just using a little bit of algebra, to this formula. 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?