So this might look like very fancy notation, but it's really just saying, add up your data points and divide by the number of data points you have. And this capital Greek letter, sigma, literally means sum, sum all of the x i's from x sub one all the way to x sub n, and then divide by the number of data points you have. Now let's think about how we would denote the same thing, but instead of for the sample mean, doing it for the population mean. So the population mean, they will denote it with mu. We already talked about that. And here, once again, you're gonna take the sum, but this time it's going to be the sum of all of the elements in your population. So your x sub i's, and you'll still start at i equals one, but it usually gets denoted that, hey, you're taking the whole population.