- A Grocery store operates with 3 check-out counters. The manager uses the following schedule to determine the number of counters in operation, depending on the number of customers in line. \begin{tabular}{|l|l|} \hline Number of customers in store & Number of counters in operation \\ \hline 1 to 3 & 1 \\ \hline 4 to 6 & 2 \\ \hline More than 6 & 3 \\ \hline \end{tabular} Customers arrive in the counters according to Poisson distribution with mean rate of 10/Hr. The average checkout per customer is exponential with mean 12 mins. Determine the expected number of idle counters