This equation computes the probability that there are exactly n units in the system (`P_n` ) for the case of a single server model (s = 1) with exponential service time, M = `oo`.
`P_n` =( 1 - `rho`)/`rho^n` = `P_0``rho^n` , where
`rho` = service utilization factor
`P_0` is the Probability there are no units in the system
This equation, Probability of n units in system (v2), s = 1, references 1 page