He decides to test his null hypothesis is that the mean number of years of experience is five years and his alternative hypothesis is that the true mean years of experience is less than five years using a sample of 25 teachers. His sample mean was four years and his sample standard deviation was two years. Rory wants to use these sample data to conduct a t-test on the mean. Assume that all conditions for inference have been met. Calculate the test statistic for Rory's test. So I always just like to remind ourselves what's going on. So you have your null hypothesis here that the mean number of years of experience for teachers in the district is five and then the alternative hypothesis is that the mean years of experience is less than five for teachers in the district.