A quality analyst wants to construct a sample mean chart for controlling a packaging process. He knows from experience that package weight is norma distributed with a mean of $20$ ounces and a standard deviation of two ounces whenever this process is in control. Each day last week, he randomly selected four packages and weighed each:

$\backslash$table$[[$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 $($using average samples weight for each day$),$ does the process appear to be out of control?