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 with the following results:

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 $23$ and $17$ ounces, on what day$($s$),$ if any, does this process appear to be out of control?