Statistical Quality Control (ISS (Statistical Services) Statistics Paper IV): Questions 12  15 of 34
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Question number: 12
» Statistical Quality Control » Control Charts » Variable
Describe in Detail
a) What are control charts for Attributes?
b) A quality control inspector at the Pepsi soft drink company has taken twentyfive samples with four observations each of the volume of bottles filled. If the average range for the twentyfive samples is. 29 ounces and the average meanof the observations is 15.95 ounces, obtain 3 σ control limits for ?
Explanation
a) To measure the quality characteristics, Control charts for attributes are used, that are counted rather than measured. Pcharts and Ccharts are common types of control charts used to measure the attributes.
Pcharts measure the proportion of items in a sample that are defective. For example, proportion of broken eggs
Question number: 13
» Statistical Quality Control » Control Charts » Variable
Describe in Detail
Following data gives the diameter of the rings manufactured by a company. Obtain the control limits for R Chart?
Sample No.

Observations
 
1

5.02

5.01

4.94

4.99

4.96

2

5.01

5.03

5.07

4.95

4.96

3

4.99

5.00

4.93

4.92

4.99

4

5.03

4.91

5.01

4.98

4.89

5

4.95

4.92

5.03

5.05

5.01

6

4.97

5.06

5.06

4.96

5.03

7

5.05

5.01

5.10

4.96

4.99

8

5.09

5.10

5.00

4.99

5.08

9

5.14

5.10

4.99

5.08

5.09

10

5.01

4.98

5.08

5.07

4.99 
Explanation
Sample No.

Observations

Range
 
1

5.02

5.01

4.94

4.99

4.96

0.08

2

5.01

5.03

5.07

4.95

4.96

0.12

3

4.99

5.00

4.93

4.92

4.99

0.08

4

5.03

4.91

5.01

4.98

4.89

0.14

5

4.95

4.92

5.03

5.05

5.01

0.13 
Question number: 14
» Statistical Quality Control » Control Charts » Variable
Describe in Detail
What are control charts for variables? Find 3 σ control limits on the chart. If we are given that μ=15.95 σ = 0.14 and n = 4 construct control limits for ?
Explanation
Control chart for variables are used to monitor characteristics that can be measured, e. g. length, weight, diameter, time etc. When a record is made of an actual measured quality characteristic like dimension expressed as hundredths of a millimeter, the quality is expressed by variables. For quality control of such
Question number: 15
» Statistical Quality Control » Control Charts » Attributes
Describe in Detail
The following are figures of defective bulbs in 10 lots each containing 30 bulbs. Construct 3σ control limits for the pchart.
Sample

No. of defective (d)

1

1

2

3

3

3

4

1

5

0

6

5

7

1

8

1

9

1

10

1 
Explanation
We have n = 30
Sample

No. of defective (d)


1

1

0.033

2

3

0.100

3

3

0.100

4

1

0.033

5

0

0.000

6

5

0.167

7

1 