Now, the last thing I wanna do is introduce you to some of the notation that you might see in a statistics textbook that looks very mathy and very difficult. But hopefully, after the next few minutes, you'll appreciate that it's really just doing exactly what we did here, adding up the numbers and dividing by the number of numbers you had. If you had to do the population mean, it's the exact same thing, it's just many, many more numbers in this context, you would have to add up 150 million numbers and divide by 150 million. So how do mathematicians talk about an operation like that, adding up a bunch of numbers and then dividing by the number of numbers? Well, let's first think about the sample mean, the sample, well, the sample mean, because that's where we actually did the calculation. So a mathematician might call each of these data points, they'll call it, let's say they'll call this first one right over here, they'll call this x sub one, they'll call this one x sub two, they'll call this one x sub three, they'll call this one, when I say sub, I'm literally saying subscript one, subscript two, subscript three. They could call this x subscript four, they could call this x subscript five, and so if you had n of these, you would just keep going, x subscript six, x subscript seven, all the way to x subscript n. And so to take the sum of all of these, they would denote it as the sum, let me write it right over here, so they will say that the sample mean is equal to the sum, the sum of all of my x sub i's, my x sub i's, so the way you can conceptualize it, these i's will change, so the i's are going to, in this case, the i started at one, the i's are going to start at one until the size of our actual sample, so all the way until n. In this case, n was equal to five.