- #1
skwey
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Homework Statement
3 people John, Paul and Naomi enter simultaniously a postoffice. There are only 2 clerks there, john and paul go first. The service time is exponentially distributed with parameters lamda1 and lamda2. Naomi must wait uintil either John or Paul is finised.
The time that Naomi spends in the post office is less than for John or Paul provided that
max(lamda1,lamda2)>c*min(lamda1,lamda2) for some constant c. What is this constant?
Homework Equations
E(X1)=1/lamda1, E(X2)=1/lamda2, x1 and x2 are the service times
I also use P(clerk one finish first)=P(X1>X2)=X1/(x1+X2)
The Attempt at a Solution
I tried to do this by saying that the expected service time for Naomi has to be less than the expected service time for the "oponent", this is the person of John or Paul left standing. I compare expected values from when Naomi starts, because it is a meomryless distribution. So when Naomi is serviced I can say that the oponents distribution starts from scratch. The oponent can be either John or Paul, depending on who finishes first.
E(Naomi service time-oponent service time)=
E(Naomi service time-oponent service time|Naomi gets service with the fastest clerk)*P(Naomi gets service with the fastest clerk)+
E(Naomi service time-oponent service time|Naomi gets service with the slowest clerk)*P(Naomi gets service with the slowest clerk)
=
max(lamda1,lamda2)/(lamda1+lamda2)*[1/max(lamda1,lamda2)-1/min(lamda1,lamda2)]
+min(lamda1,lamda2)/(lamda1+lamda2)*[1/min(lamda1,lamda2)-1/max(lamda1,lamda2)]
I say that this has to be less than 0 (<0) because then it means that Naomi has the lowest extected time
this gives max(lamda1,lamda2)>min(lamda1,lamda2)
so c=1
But the answer is supposed to be 2-sqrt(3),can anyone please help?