Phone calls following Poisson process

endlessend2525

New member
Joined
Dec 19, 2016
Messages
2
I struggle with a problem of conditional probability:

I know that phone calls arrive according to a Poisson process with rate 2.
If I know that up to time t = 1 there is one call only, how likely is it that it arrived after t = 0.75 ?
If I know that up to time t = 1 two calls arrived, how likely is it that the second arrived after t = 0.75 ?

So for the first problem I set that
P(S1>0.75/X(1)=1), with S1S1, the time it takes for the first event to occur, and X(1)X(1), the number of events that occurred up to time 1. But then I don't quite see how to handle it.
I need to use the following information that

[X(1)=1]=[S11<S2]
P(0.75<S11<S2) / P(S11<S2)
But I don't quite see the idea behind
 
Top