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What do you understand by quality control by attributes and quality control by variables? 5

  1. Where do you need a large sample size in the above and why?                              5
  2. Four batches of products are inspected at 90 minute intervals and their percentage difference in weights from the nominal are given below:

Percentage difference on weights in sample

Batch – 1

Batch – 2

Batch – 3

Batch – 4

1.2

0.6

0.6

2.1

1.8

0.3

1.5

0.6

1.5

0.3

1.0

0.6

0.9

0.0

0.0

2.7

0.3

0.6

1.9

2.7

Assume that normal process average variation is 0.9% and process standard deviation is 0.5%, range U.C.L. is 5 times S.D. Plot $\overbar{X}$, R chart indicating the various control limits. Is the process under control?

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