Answer:
2.25
Step-by-step explanation:
let: Mean arrival rate [tex]\alpha=15[/tex] and mean service rate[tex]s=20[/tex]
#First we need to calculate the average number of customers in the system [tex]N[/tex] and average time a customer spends in the system,[tex]W[/tex] as:
[tex]N=\frac{\alpha}{s-\alpha}=15/(20-15)=3\\\\\\W=\frac{N}{\alpha}=3/15=12\ mins[/tex]
The average time spend in the line is:
[tex]N_l=\alpha W_l=\alpha^2/s(s-\alpha)\\=15^2/(20\times5)\\\\=2.25[/tex]
Hence the average number of customers in a line is 2.25
