To monutor the reponse time of energency reponse teams to cakls from the local community, a $3-$sigma control chart for mean js constructrd Samples of $4$ response times are used. Their means and ranges are calculated. After $10$ such samples are collected the avergae of all ghe sample mena response times js $11\mathrm{.}3$ minutes and yhe avergae rnage js $4\mathrm{.}1$ minutes.

The upprr and lower control limits for tge mean charts are:

$14\mathrm{.}29$ and $8\mathrm{.}31$ minutes

$14\mathrm{.}29$ and $9\mathrm{.}51$ minutes

$13\mathrm{.}09$ and $8\mathrm{.}31$ minutes

$13\mathrm{.}09$ and $9\mathrm{.}51$ minutes