Question

The following data gives the average life (in hours) and a range of 12 samples of 5 lamps each. The data are 

Sample No.	1	2	3	4	5	6
Sample Mean	1080	1390	1460	1380	1230	1370
Sample Range	410	670	180	320	690	450
Sample No.	7	8	9	10	11	12
Sample Mean	1310	1630	1580	1510	1270	1200
Sample Range	380	350	270	660	440	310

Construct control charts for mean and range. 

Comment on the control limits.

Answer 1

In this question the number of observations is 5 for each sample. So we use A₂ = 0.577, D₃ = 0, D₄ = 2.114 from the table of control chart constants.

We observe that the sample \(\overline{X}\) value 1080 is below the LCL. All sample range values are within the control limits for R. We say that process is out of control.