Statistical Quality ControlControl Charts (ISS (Statistical Services) Statistics Paper IV): Questions 17  20 of 31
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Question number: 17
» Statistical Quality Control » Control Charts » Variable
Describe in Detail
a) If the average range for the 4 samples is 0.2 millimeters and the average mean of the observations is 12.5 millimeters, obtain the threesigma control limits for the sample mean.
b) 5 observations have been taken from the10 samples in order to test the volume in the bags. The average sample range is 0.5 ounces. Obtain the 3σ limits for the sample range.
Explanation
a) It is given that n = 5 and
For n = 5, The value of
Control limits for :
And
b) We are given that, number of observations, n = 5,
For n = 5, from the tables
Question number: 18
» Statistical Quality Control » Control Charts » Variable
Describe in Detail
A new oven has been installed in a bakery and to test the efficiency of this, the oven temperature readings have been taken at four different places inside the oven every 30 min. The following table gives readings. Determine the control limits for the mean temperature.
Time  Readings  
8: 00  400  500  550  390 
8: 30  440  420  380  380 
9: 00  410  450  470  430 
9: 30  390  390  410  410 
10: 00  370  420  460  410 
10: 30  390  400  390  400 
Explanation
Readings  Total  Sample mean  Sample Range  
400  500  550  390  1840  460  160 
440  420  380  380  1620  405  60 
410  450  470  430  1760  440  60 
390  390  410 
Question number: 19
» Statistical Quality Control » Control Charts » Attributes
Describe in Detail
The following are the figures of defectives in 22 lots each containing 2, 000 bulbs. Ind control limit for pChart.
425  430  216  341  225  322  280  306  337  305  356 
402  216  264  126  409  193  326  280  389  451  420 
Explanation
We have n = 2000
S. No.  d 

1  425  0.2125 
2  430  0.215 
3  216  0.108 
4  341  0.1705 
5  225  0.1125 
6  322  0.161 
7 
Question number: 20
» Statistical Quality Control » Control Charts » Attributes
Describe in Detail
Each day a sample of 1500 items from a production process was examined. The number of defectives found in each sample was as follows. With a suitable control chart, check out for control 4, 6, 6, 2, 15, 4, 4
Explanation
We have n = 30
S. No.  d 

1  4  0.00267 
2  6  0.00400 
3  6  0.00400 
4  2  0.00133 
5  15  0.01000 
6  4  0.00267 