An auditor for a hardware store chain wished to compare the efficiency of two different auditing techniques. To do this he selected a sample of nine store accounts and applied auditing techniques A and B to each of the nine accounts selected. The number of errors found in each of techniques A and B is listed in the table below:

Errors in A Errors in B

45 31

48 37

46 39

48 37

52 54

50 45

49 49

40 41

45 50

Select a 90% confidence interval for the true mean difference in the two techniques.

a) [3.050, 5.838]

b) [-4.183, 4.183]

c) [2.584, 6.304]

d) [2.195, 6.693]

e) [0.261, 8.627]

f) None of the above