 This bootcamp takes you through several mathematical concepts and techniques that you need in order to do the introduction to statistics course. Okay, as you can see, that symbol there, sigma, that's capital sigma, and we use that to denote some summations. You'll see an Excel 2 by the way. So in this example, we summed x1 plus x2 all the way through x7, and notice how simple it is when you just put a summation in front of the xi. Here's how we use the summation symbol in statistics. Note that the sample mean is the sum of all the values, sum of xi, divided by n. Also, we're going to talk about summing squared observations in the course. In the course, we're going to learn about ways to measure variation. One of them is the sample variance, where we're basically getting the deviations around the mean, squaring them, adding them up, and dividing by n minus one. We'll worry about why we're dividing by n minus one and not n once we actually get to the course. So here's just the way we worked out the problem. Remember, the numerator is the deviation from the mean. So we n square it. So that's one minus three squared, two minus three squared, and so on. When you add all of the squared deviations up, you get 10 for the numerator, and then you divide by n minus one, remember, not by n, we're dividing by four. And so we get a variance of 2.5. When you get to the point where you want to compute the standard deviation, another measure of deviation, you just take the variance and take the square root of that, and that's the standard deviation. Again, more later in the course. To find more boot camp modules, visit the stat course at the URL you see there, and go to the navigation bar on the left, click boot camp, and you'll see all kinds of things that are good to do prior to the statistics course. Many of you have already done this before and maybe only need a refresher.