Some patients have complained that the ambulances arrived very

late

after the $9-1-1$ calls were made. The Service de Police de la Ville de

Montreal

$($SPVM$)$ would like to investigate this potential problem by

developing

a control chart based on two years of monthly data for the number of

calls

whose response times were more than $10$ minutes $($termed as "late

arrivals"$).$

Assuming the average number of late arrivals $=2\mathrm{.}79,$ determine control

limits

for an appropriate control chart $($with $3-$sigma limits$)$ to monitor the

situation.