Poisson Event After Time Interval

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So I have this Poisson Problem that I'm struggling with, and the basis is that you have a server that fails once every four hours (so the average is 1/4 of a crash per hour). The question that I'm really struggling with Is: "What is the probability of a third system crash happening after the first 8 hours". I have no idea how to solve it since it doesn't specify a closed interval. Thanks.

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Assuming the question is asking the probability that the third crash happens after the $8$ hour mark (which is to say, it does not happen before the 8 hour mark), this is just the probability that two or fewer crashes occur in the first eight hours. So there's your closed interval.

The number of crashes $N$ in the first eight hours is Poisson distributed with mean $\lambda=2,$ so you just need to compute the probability of two or fewer crashes, $P(N\le 2).$