A maintenance service facility has Poisson arrival rates,

A maintenance service facility has Poisson arrival rates, negative exponential service time and operates on a 'first come first served' queue discipline. Break-downs occur on an average of 3 per day with a range of zero to eight. The maintenance crew can service an average of 6 machines per day with a range of zero to seven. The mean waiting time for an item to be serviced would be

Given: λ = 3 per day (arrival rate)
μ = 6 per day (service rate)
Mean waiting time for an item to serviced

=	λ	=	3	=	1	×	1	=	1	day.
	μ(μ − λ)		6(6 − 3)		2		3		6