So I don't want you to worry too much about that just now. But if you are going to go further in statistics, I just want to make that clarification. Now, the population mean, or the arithmetic mean, of this data set right here, it is negative 10 plus 0 plus 10 plus 20 plus 30 over, we have 5 data points, over 5. And what is this equal to? That negative 10 cancels out with that 10. 20 plus 30 is 50. Divided by 5, it's equal to 10.