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, .02. A letter is defective when one or more errors are detected.
A. Calculate the control limits for a p chart. B. A sample of 400 letters has just been taken, and 6 letters are defective. Is the process still in control?