The IRS is concerned with improving the accuracy of tax information given by its representatives over the telephone. Previous studies involved asking a set of 25 questions of a large number of IRS...

The IRS is concerned with improving the accuracy of tax
information given by its representatives over the telephone.
Previous studies involved asking a set of 25 questions of a
large number of IRS telephone representatives to determine
the proportion of correct responses. Historically, the aver-
age proportion of correct responses has been 72 percent.
Recently, IRS representatives have been receiving more
training. On April 26, the set of 25 tax questions were again
asked of 20 randomly selected IRS telephone representatives.
The numbers of correct answers were 18, 16, 19, 21, 20, 16,
21, 16, 17, 10, 25, 18, 25, 16, 20, 15, 23, 19, 21, and 19.
a. What are the upper and lower control limits for the
appropriate p-chart for the IRS? Use z = 3.
b. Is the tax information process in statistical control?