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# poisson watch

1. Hi

Really stuck on some easy Poisson activity questions. If I am told that a certain tree in a square km has a Poisson density of 21 per sq km. I can work out the probability of there being zero instances of that certain tree; p (X = 0) = Po(21) = 7.583 x 10^-10. But how does this help me in finding the expected distance of that particular tree? I am missing something fundamental here and for the life of me cannot get my head around such an easy problem. Thanks for any pointers that anyone can throw my way. Cheers
2. (Original post by Nick_J)
Hi

Really stuck on some easy Poisson activity questions. If I am told that a certain tree in a square km has a Poisson density of 21 per sq km. I can work out the probability of there being zero instances of that certain tree; p (X = 0) = Po(21) = 7.583 x 10^-10. But how does this help me in finding the expected distance of that particular tree? I am missing something fundamental here and for the life of me cannot get my head around such an easy problem. Thanks for any pointers that anyone can throw my way. Cheers
Can you put up the complete question please?

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