And these calculations on the entire population, sometimes you might be able to do it, oftentimes you will not be able to do it, these are called parameters. This is called parameters. So what you're going to find in much of statistics, it's all about calculating statistics for a sample, finding these sample statistics in order to estimate parameters for an entire population. 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?