The standard deviation of our distribution, of the difference of the mean, the distribution of the difference of the sample means, is going to be equal to the square root of the variance of our first population. Now the variance of our first population, we don't know it, but we can estimate it with our sample standard deviation. If you take your sample standard deviation, 4.67, and you square it, you get your sample variance. So this is the variance, this is our best estimate, of the variance of the population. And we want to divide that by the sample size. And then plus our best estimate of the variance of the population of group 2, which is 4.04 squared, the sample standard deviation of group 2 squared, that gives us the variance, divided by 100. And this gives us, I did it before in the last, maybe it's still sitting on my calculator.