Nontraditional university students, generally defined as those at least 25 years old, comprise an increasingly large proportion of undergraduate student bodies at most universities. A study reported in the College Student Journal (Dec. 1992) compared traditional and nontraditional students on a number of factors, including grade point average (GPA). The table below summarizes the information from the sample.

G PA Traditional Students Nontraditional Students

a. What are the appropriate null and alternative hypotheses if we want to test whether the mean GPAs of traditional and nontraditional students differ'?

b. Conduct the test using a = .01, and interpret the result.

c What assumptions are necessary to ensure the validity of the test'?