In this tutorial, I'm going to talk about calculating the standard deviation and variance. They are both related. This isn't high definition, so click on 720 before you click the fullscreen view. The button is right there. A typical problem looks like this: the following are the number of jobs a sample of six people applied for. Find the mean, the variance, and standard deviation. Blah blah blah, what you really are interested in are just the numbers and how to calculate the variance and standard deviation, and that's what I'm going to do here. The sample standard deviation is equal to the square root of the sample variance, and these are the symbols I'm going to use. The first thing I'm going to calculate is the sample variance. The sample variance is this formula right here, and we'll take the square root of that to get the standard deviation. The X i, that's the observations, the x-bar, that's the mean, and we'll go through the calculations of each one of these two. N is the sample size. I'm going to make a little table to help me stay organized, and I recommend that you do the same. I'm gonna put in the X which is my observation, and then we'll put a little horizontal line and I'm gonna do an up-and-down vertical line as well. The next column is the mean, x-bar. That's the sample mean. Put a little vertical line as well. Now I'll just put in all the observations, and that's the same as above, a line. And I'm gonna put a couple more column headings in and I'll tell you what those mean as we fill them in, but just go ahead and write them in now. That's the observation minus the mean squared. So, I need to calculate...