Quality and Reliability · Quality Management · 1 mark · Numerical answer
Thirty samples of size 100 contain 420 total nonconformities. Find the lower control limit of the control chart for number of nonconformities, to two decimals.
For constant sample size use a c-chart. Mean count per sample is $\bar c=420/30=14$. Three-sigma lower limit is $\max(0,\bar c-3\sqrt{\bar c})=14-3\sqrt{14}=2.7750$. **2.78 nonconformities/sample**.
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