A store currently operates its service system with $1$ operator. Arrivals follow a Poisson distribution and service times are exponentially distributed. The following spreadsheet has been developed for the system.

Arrival rate $6$

Service rate $8$

Number of servers $1$

Utilization $75\mathrm{.}00\%$

P$(0),$ probability that the system is empty $0\mathrm{.}2500$

Lq$,$ expected queue length $2\mathrm{.}2500$

L$,$ expected number in system $3\mathrm{.}0000$

Wq$,$ expected time in queue $0\mathrm{.}3750$

W$,$ expected total time in system $0\mathrm{.}5000$

Probability that a customer waits $0\mathrm{.}7500$

$17.$ What is the probability that a customer must wait in queue before being served?

a$.0\mathrm{.}00$

b$.0\mathrm{.}25$

c$.0\mathrm{.}75$

d$.1\mathrm{.}00$

$18.$ What is the probability that a customer can go directly into service without waiting in line?

a$.0\mathrm{.}00$

b$.0\mathrm{.}25$

c$.0\mathrm{.}75$

d$.1\mathrm{.}00$

$19.$ How many customers will be in the system on average at any one time?

a$.0\mathrm{.}375$

b$.0\mathrm{.}50$

c$.2\mathrm{.}25$

d$.3\mathrm{.}00$

$20.$ What is the expected number of minutes a customer actually will be served?

a$.45$

b$.7\mathrm{.}5$

c$.30$

d$.22\mathrm{.}2$

$21.$ If the store adds an additional server to its system, what happens to a customer's average service time?

a$.$ increases

b$.$ decreases

c$.$ it is unchanged

d$.$ depends on the arrival rate