Well, the standard deviation of the differences of the sample means is going to be equal to, and we saw this in the last video. In fact, I think I have it right at the bottom here. It's going to be equal to the square root of the variances of each of those distributions. Or the variance of this distribution is going to be equal to the sum. Let me write it this way, right over here. So the variance, I'll re-kind of prove it. The variance of the means, or the variance of our distribution, is going to be equal to the sum of the variances of each of these sampling distributions.