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Average time in system: 0.067 hour
=== Relation for Mean Waiting Time in M/M/1 and M/D/1 queues
For an equilibrium M/G/1 queue, the expected value of the time W spent by a customer in the queue are given by Pollaczek-Khintchine formula as below<ref name=":0">{{Cite book|title=Introduction to Queuing Theory|last=Cooper|first=Robert B.|publisher=Elsevier Science Publishing Co.|year=1981|isbn=0-444-00379-7|___location=|pages=189}}</ref>:
<math>E(W)=\frac{\rho\tau}{2(1-\rho)}(1+\frac{\sigma^2}{\tau^2})</math>
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where τ is the mean service time; <math display="inline">\sigma^2</math> is the variance of service time; and ρ=λτ < 1, λ being the arrival rate of the customers.
For M/M/1 queue, the service times are exponentially distributed, then <math display="inline">\sigma^2</math>=<math display="inline">\tau^2</math> and the mean waiting time in the queue denoted by W<sub>M</sub> is given by the following equation<ref name=":0" />:
<math>{W_M}=\frac{\rho\tau}{1-\rho}</math>
Using this, the corresponding equation for M/D/1 queue can be derived, assuming constant service times. Then the variance of service time becomes zero, i.e. <math display="inline">\sigma^2</math>=0. The mean waiting time in the M/D/1 queue denoted as W<sub>D</sub> is given by the following equation<ref name=":0" />:
<math>{W_D}=\frac{\rho\tau}{2(1-\rho)}</math>
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