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 3σ 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?