.(i) What do you understand by quality control by attributes and Q.C by variables ?
(ii) Where do you need a larger sample size in the above and why? 4 batches of products are inspected at 90 minute intervals and their percentage differences in weight from the nominal are given below.
|
Percentage difference on weight in samples
|
|
Batch or Sample 1
|
Sample 2
|
Sample 3
|
Sample4
|
|
1.2
1.8
1.5
0.9
0.3
|
0.6
0.3
0.3
0.0
0.6
|
0.6
1.5
1.0
0.0
1.9
|
2.1
0.6
0.6
2.7
2.7
|
Assume that normal process average variation is 0.9% and process standard deviation is 0.5%. Assume further that range U.C.L is 5times S.D. Plot the 
chart indication the various control limits.
(iii) Is the process under control? Any comments