A quality analyst wants to construct a sample mean chart for controlling a packaging process. He kno

A quality analyst wants to construct a sample mean chart for controlling a packaging process. He knows
from past experience that when the process is operating as intended, packaging weight is normally
distributed with a mean of twenty ounces, and a process standard deviation of two ounces. Each day
last week, he randomly selected four packages and weighed each. The data from that activity appear
below.
  see the document I uploaded
(a)
If he sets an upper control limit of 21 and a lower control limit of 19 around the target value of
twenty ounces, the control chart is based on what value of
z
?
(b)
With the UCL and LCL of part a, what do you conclude about this process–is it in control?