Problem 2: Five data entry operators work at the data processing department of t
ID: 330851 • Letter: P
Question
Problem 2:
Five data entry operators work at the data processing department of the Georgia Bank. Each day for 10 days, the number of defective records in a sample of 200 records typed by these operators has been noted, as follows:
Sample
1
2
3
4
5
6
7
8
9
10
No. of Defectives
19
25
28
12
14
8
25
10
16
6
What SPC chart is needed here?
Using z=3, establish upper and lower control limits for the control chart and judge if the process is in control.
Sample
1
2
3
4
5
6
7
8
9
10
No. of Defectives
19
25
28
12
14
8
25
10
16
6
Explanation / Answer
p chart is needed here to compute the control limit
p-bar = total number of defectives/Total sample size = 163/(10*200) = 0.0815
standard deviation (s) = sqrt(p-bar*(1-p-bar)/n)
n = 200
s = sqrt(0.0815*(1-0.0815)/200) = 0.0193
z = 3
UCL = p-bar + z*s = 0.0815 + 3*0.0193 = 0.1394 or 0.1394*200 = 27.88
LCL = p-bar - z*s = 0.0815 - 3*0.0193 = 0.0236 = 4.72
Hence, number of defects can be in range of 5 to 27
So, process is in control
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