From this 20, she calculates a sample mean of 38.75. Now ideally, she wants to construct a t-interval, a confidence interval using the t-statistic. And so that interval would look something like this. It would be the sample mean, plus or minus the critical value, times the sample standard deviation divided by the square root of n. And we use a t-statistic like this, and a t-table, and a t-distribution when we are trying to create confidence intervals for means where we don't have access to the standard deviation of the sampling distribution, but we can compute the sample standard deviation. Now in order for this to hold true, there's three conditions, just like what we saw when we thought about z-intervals. The first is, is that our sample is random. Well, they tell us that here, that she took a simple random sample of 20.