Five data entry operators work at the data processing department of the Birmingham Bank. Each day for 30 days, the number of defective records in a sample of 250 records typed by these operators has been noted, as follows:

SAMPLE NO.

NO.

DEFECTIVE SAMPLE NO.

NO.

DEFECTIVE SAMPLE NO.

NO.

DEFECTIVE 1 7 11 18 21 17 2 5 12 5 22 12 3 19 13 16 23 6 4 10 14 4 24 7 5 11 15 11 25 13 6 8 16 8 26 10 7 12 17 12 27 14 8 9 18 4 28 6 9 6 19 6 29 12 10 13 20 16 30 3

a) Establish 3s upper and lower control limits.

b) Why can the lower control limit not be a negative number?

c) The industry standards for the upper and lower control limits are 0.10 and 0.01, respectively. What does this imply about Birmingham Bank’s own standards?