So let's look it up for 97.5% on our z-table. Let's see, we have 97 right here. This is 0.975, or 97.5. And this gives us a z-value of 1.96. So this is z is equal to 1.96. Or, only 2.5% of the results, or of the samples from this population, are going to be more than 1.96 standard deviations away from the mean. So this critical z-value right here is 1.96 standard deviations.