A standard measure of aggression in 7-year-old children has been found to have a 20% trimmed mean of 4.8 based on years of experience. A psychologist wants to know whether the trimmed mean for children with divorced parents differs from 4.8. Suppose X¯t = 5.1 with sw = 7 based on n = 25.

Test the hypothesis that the population trimmed mean is exactly 4.8 with α = .01.