Question

A Quality Analyst wants to construct a sample mean chart for controlling a packaging process. He knows from past experience that whenever this process is under control, package weight is normally distributed with a mean of twenty ounces and a standard deviation of two ounces. Each day last week, he randomly selected four packages and weighed each:
Day WEIGHT (ounces)
Monday 23 22 23 24
Tuesday 23 21 19 21
Wednesday 20 19 20 21
Thursday 18 19 20 19
Friday 18 20 22 20
If he uses upper and lower control limits of 22 and 18 ounces, on what day(s), if any, does this process appear to be out of control?
a) Monday
b) Tuesday
c) Monday and Tuesday
d) Monday, Tuesday, and Thursday
e) none

Answer 1

On Monday and Tuesday, the process appears to be out of control.                                                                                                                                                

Explanation:

• There are five days Monday, Tuesday,Wednesday, Thursday and Friday. Monday and Tuesday have weight up to 21. Wednesday weights up to 21.
• Thursday and Friday weigh up to 20. Except for Monday and Tuesday, all the days have packaged up to the value of  21. So Monday and Tuesday are the days that appear to be out of control.
• On checking the package for each day he came to know that Monday and Tuesday have process out of control.