Refer to Exercise 1. Based on independent random samples of 20 students from each group, the average midterm exam score for the regular attendees and the absent students were 70.5% and 61.8%, respectively.

The population standard deviation for both groups is 12% and the grades are normally distributed.

At the 5% level of significance, is there sufficient evidence to conclude that, on average, regular attendees perform

(a) better than non-attendees? (b) more than three percentage points better than non-attendees?