A production plant checks 150 particular modules for quality control purpose eve

Question

A production plant checks 150 particular modules for quality control purpose every day. The inspector collects following data on the number of modules failed the inspection in the past few days. day No. of failed modules Please recommend an appropriate control charts). What are the control limits for such control hart using 2-sigma LCL, UCL]? Is the process in control? (keep three decimal places if necessary) Select one: a. [0.067, 0.173]; in control O b. [o.093, o.147); Not in control O O c. (o.067, 0.173); Not in control d. 19.5, 25.4): Not in control e. [0.040, o.200]; in control t of

Explanation / Answer

The control chart I would suggest is P-chart. P-charts are generally used when it is easy to distinguish between a defective and non-defective item. In this case, it would be modules failed.

Sample size during the periods remains same. Here, N= 150. Total Sample size = 750

Sum of all modules failed = 90

Proportion of modules failed,p = (90/750) = 0.12

?p= Sqrt (p(1-p)/ n) = sqrt (0.12*0.88/150) = 0.0265

Z = 1.96 for 2 control limits

UCL = p + z*?p = 0.173

LCL = p - z*?p = 0.067

Range is 0.067 - 0.173, for sample size 4, proportion of modules failed = 5/150 = 0.033 , This is outside the control limits.Hence, Correct answer is C and process is not in cotnrol.

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