13. The task in a particular concept-formation experiment is to discover, through trial and error, the correct sequence in which to press a row of buttons. It is determined from the nature of the task that the average score obtained by random guessing alone would be 20 correct out of a standard series of trials. The following are the scores for a sample of volunteer college students: 31, 24, 21, 25, 32. You wish to determine whether such subjects do better, on the average, than expected by just guessing.

(a) Set up H0 and H1.

(b) Determine t.05.

(c) Perform the statistical test.

(d) Draw final conclusions.