# Statistical Quality Control-Control Charts (ISS (Statistical Services) Statistics Paper IV): Questions 21 - 22 of 31

Get 1 year subscription: Access detailed explanations (illustrated with images and videos) to 79 questions. Access all new questions we will add tracking exam-pattern and syllabus changes. View Sample Explanation or View Features.

Rs. 300.00 or

## Question number: 21

» Statistical Quality Control » Control Charts » Variable

Essay Question▾

### Describe in Detail

a) The number of customer complaints are recorded at a television manufacturing company. Complaints have been recorded over the past 20 weeks. Construct 3-σ control limits for the c-chart.

 Week No. of complaints Week No. of complaints 1 0 11 4 2 3 12 3 3 4 13 1 4 1 14 1 5 0 15 1 6 0 16 0 7 3 17 2 8 1 18 1 9 1 19 2 10 0 20 2

b) A machine is manufacturing mica discs. samples of size 5 are drawn every hour and their thickness in units are recorded as follows. From this data construct 3-σ control limits for chart.

 Sample No. Observstions 1 8 9 15 4 11 2 7 10 7 6 8 3 11 12 10 9 10 4 12 8 6 9 12 5 11 10 6 14 11 6 7 7 10 4 11 7 10 7 4 10 10 8 8 11 11 7 7 9 8 11 8 14 12 10 12 9 12 17 11 11 7 7 9 17 13 12 9 9 4 4 11 13 10 12 12 12 12 14 8 11 9 6 8 15 10 13 9 4 9 16 9 11 8 5 11

### Explanation

a) Average number of defects per sample is

=1.5+ =1.5 + 3 (1.22) =5.174

= →0

Since number of defects cannot be negative, can be considered as zero. (rounded up to zero)

b) Second question:

 Sample No. Observations Total Sample Mean Sample Range 1 8 9 15 4 11 47 9.4 11 2 7 10 7 6 8 38 7.6 4 3 11 12 10 9 10 52 10.4 3 4 12 8 6 9 12 47 9.4 6 5 11 10 6 14 11 52 10.4 8 6 7 7 10 4 11 39 7.8 7 7 10 7 4 10 10 41 8.2 6 8 8 11 11 7 7 44 8.8 4 9 8 11 8 14 12 53 10.6 6 10 12 9 12 17 11 61 12.2 8 11 7 7 9 17 13 53 10.6 10 12 9 9 4 4 11 37 7.4 7 13 10 12 12 12 12 58 11.6 2 14 8 11 9 6 8 42 8.4 5 15 10 13 9 4 9 45 9 9 16 9 11 8 5 11 44 8.8 6 Total 150.6 102

… (126 more words) …

## Question number: 22

» Statistical Quality Control » Control Charts » Variable

Essay Question▾

### Describe in Detail

When should R-Chart be Analyzed? Six samples which contain 20 observations per sample have been collected and the sample means and sample ranges are computed as shown below. Test whether the sample means are within control limits of ?

 Sample Mean Range 1 3.06 0.42 2 3.15 0.5 3 3.11 0.41 4 3.13 0.46 5 3.06 0.46 6 3.09 0.45

### Explanation

• Range chart should be analyzed before the mean chart since variability of the process must be in control before the mean chart can be analyzed.

• If the R chart indicates that the dispersion of the quality by the process is out of control, generally it is better not to construct chart, until the quality dispersion is brought under control

… (66 more words) …

f Page