The instructor of an introductory psychology course is interested in knowing if there is a difference in the mean grades on the final exam between the fall (Xm=82.4, n=150, S²=11.56) and winter (Xm=84.2, n=150, S²=11.44) classes.

a) What are the H0 and Ha? Is Ha one-tailed or two-tailed?

b) What specific test should we use?

c) After calculation, t=-4.62 and tcv=1.645, what conclusion we can make?

d) The 95% confidence interval is computed based on the formula of CI₉₅ = (Xm1-Xm2)(tcv)(Standard error of Xm1-Xm2). After calculation, the CI₉₅ is 0.74.90, how do you interpret it?