We're taking this minus this squared for each of these data points. And then finally, we'll do that with the last group. Sample mean is 6. So it's going to be 6 minus 4 squared plus 6 minus 4 squared plus 6 minus 4 squared. Now let's think about how many degrees of freedom we had in this calculation right over here. How many degrees of freedom? Well, in general, I guess the easiest way to think about it is how much information did we have, assuming that we knew the mean of means.