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
25	11
28	17
26	19
28	17
32	34
30	25
29	29
20	21
25	30

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