We have taken 12 samples of 400 letters each from a typing pool and found the following proportions of defective letters: 01, .02, .02, .00, .01, .03, .02, .01, .00, .04, .03 and .02. A letter is considered defective when one or more errors are detected.
1. Calculate the center line, upper and lower control limits for a p chart. Show your work; use an alternative symbol for the square root sign if you need to.
2. Create a control chart using your results and plot your observational values of defective letters.
3. Is this process stable or unstable (in or out of control)? How come?
A p chart with control limits (upper and lower) has been constructed and plotted.