The dean of a large college is concerned that the students' grade-point averages have changed dramatically in recent years. The graduating seniors' mean GPA over the past five years is 2.75. The dean randomly samples 256 seniors from the last graduating class and finds that their mean GPA is 2.85, with a standard deviation of 0.65. Test if the dean's concern s right or not. (alpha=0.05)

a) What is the null and alternative hypothesis?

b) Is it a directional or non-directional test?

c) What specific test should we use?

d)After calculation, t_cv=1.96, t=2.463 with p=0.014, what we can conclude?