Answer:2 min
Explanation:
Given
Arrival rate [tex]\lambda =\frac{60}{1}[/tex] per hour
Service rate [tex]\mu =\frac{60\times 60}{40}[/tex] per hour
[tex]\rho =\frac{\lambda }{\mu }=\frac{40}{60}=\frac{2}{3}[/tex]
Now average waiting time in the system is given by
waiting time [tex]L_s=\frac{1}{\mu -\lambda }[/tex]
[tex]L_s=\frac{1}{90-60}=\frac{1}{30} hr[/tex]
[tex]L_s=\frac{60}{30}=2 min[/tex]