So let's try to take each of these data points and find the difference. Let me do that in a different color. Each of these data points and find the difference between that data point and our sample mean, not the population mean. We don't know what the population mean. The sample mean, so that's that first data point plus the second data point plus the second data point. So it's 4 minus 2 squared plus 1 minus 2 squared. And this is what you would have done if you were taking a population variance.