Calculating the probability of an event occurring in a specific time periodI am confused at how to approach the following question, i.e. what probability formula I am supposed to use.If the probability of a flood is 0.12 during a year, what is the probability of two floods over the next 10 years...?I have thought perhaps trying Geometric distribution at first, but it didn't seem to work out properly. I also tried Poisson, but it turned out to be quite a small number... which doesn't seem viable.So my question is, how can I go about solving this and which probability distribution am I supposed to use?

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Calculating the probability of an event occurring in a specific time periodI am confused at how to approach the following question, i.e. what probability formula I am supposed to use.If the probability of a flood is 0.12 during a year, what is the probability of two floods over the next 10 years...?I have thought perhaps trying Geometric distribution at first, but it didn&#039;t seem to work out properly. I also tried Poisson, but it turned out to be quite a small number... which doesn&#039;t seem viable.So my question is, how can I go about solving this and which probability distribution am I supposed to use?

akademiks1989rz · Accepted Answer

Step 1If it is only possible to flood once a year if at all (like the Nile) but not twice, then you are looking at a binomial with   n  =  10 and   p  =  0.12 in either                              (                            n        2                              )                          p    2    (  1  −  p      )          n      −      2      or   1  −      p    0    (  1  −  p      )          n      −      0        −  n      p    1    (  1  −  p      )          n      −      1      Step 2depending on whether you want exactly or at least 2 floods in 10 years.

Shannon Andrews · Accepted Answer

Step 1Assuming you could have more than 1 flood per yearThe expected value   →  E  (  x  )  =  λ  10  =  for 10 years  =  λ  1  ⋅  10  =  0.12  ⋅  10  =  1.2 floods in a 10 year period.Step 2So then rerun Poisson&#039;s for this new period of 10 years with   =  2  →  P  (  2  )  =  (      1.2          2        )      e          (      −      1.2      )              /            2      !        =  0.216859  =  21.69  % chance of getting EXACTLY 2 floods over 10 years.

Calculating the probability of an event occurring in a specific time period

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