A Quality Analyst wants to construct a control chart for determining whether three machines, all producing the same product, are under control with regard to a particular quality variable. Accordingly, he sampled four units of output from each machine, with the following results:

$\backslash$table$[[$Machine$,,$sure,,$],[$#$1,17,15,15,17],[$#$2,16,25,18,25],[$#$3,23,24,23,22]]$

Using the factors for three sigma control limits$,$ what are the $x-$bar chart upper and lower control limits$?$

Select one:

a$.24\mathrm{.}33$ and $15\mathrm{.}67$

b$.23\mathrm{.}5$ and $16\mathrm{.}5$

c$.23\mathrm{.}16$ and $16\mathrm{.}84$ Well done!

$$ d$.23\mathrm{.}29$ and $16\mathrm{.}71$