Last year, there were 30,000 students at a university; their GPA had a mean of 2.9 and an SD of 0.6. This year, in a simple random sample of 100 students taken from this university, the GPAs have a mean of 2.95 and an SD of 0.55. Has the mean GPA at the university gone up since last year, or is this just chance variation? Pick the correct calculation of the test statistic.
one-sample z = (2.95 - 2.9)/0.06 = 0.833; P large; conclude chance variation one-sample z = (2.95 - 2.9)/0.055 = 0.909; P large; conclude chance variation two-sample z = (0.05 - 0)/sqrt(0.055^2 + 0.0035^2) = 0.907; P large;

Question

Last year, there were 30,000 students at a university; their GPA had a mean of 2.9 and an SD of 0.6. This year, in a simple random sample of 100 students taken from this university, the GPAs have a mean of 2.95 and an SD of 0.55. Has the mean GPA at the university gone up since last year, or is this just chance variation? Pick the correct calculation of the test statistic.
one-sample z = (2.95 - 2.9)/0.06 = 0.833; P large; conclude chance variation one-sample z = (2.95 - 2.9)/0.055 = 0.909; P large; conclude chance variation two-sample z = (0.05 - 0)/sqrt(0.055^2 + 0.0035^2) = 0.907; P large;