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\subsection{Question b}  Out of the peak hour the traffic intensity decreases to $a = 3$ \textit{Erlangs}\footnote{$2$ groups per minute times $1.5$ minutes service time}. Already with $c=5$ elevators the average server utilization is low: $\rho = 3/5 = 0.6$. The average waiting time \eqref{Tim} is $T_w=11''$, that is, it is very small compared to the average service time ($W_s=1'$ $30''$). Thanks to one additional elevator, the average server utilization could be made as small as $\rho=0.5$, lowering the average waiting time \eqref{Tim} to $T_w=3''$. Also in this case the decrease in waiting time is much more than proportional w.r.t the increase in the number of elevators. However, the time needed on average by the employees to reach their floors does not decrease significantly: from $1'$ $41''$ to $1'$ $33''$. We conclude that it wouldn't be useful for corporate B to keep in service the additional elevator also in this case.