# Thread: Determining how to find the prob. an event will occur between 2 yrs. (Poisson dist.)

1. ## Determining how to find the prob. an event will occur between 2 yrs. (Poisson dist.)

Hello! I am having trouble with the following question regarding the Poisson distribution. I was thinking that lambda is (2.5/100)(25). I'm not really sure if this question relates to the exponential distribution or Poisson distribution because of the fact that it asks for the probability the event will happen between the two years. I am not allowed to use any special calculator program to find the answer in my class. Thanks for your help.

Question: Volcanic eruptions of Mt. Vesuvius follow a Poisson distribution with an average of 2.5 eruptions every 100 years. Find the probability that the next eruption will occur between 25 and 50 years.

2. ## Re: Determining how to find the prob. an event will occur between 2 yrs. (Poisson dis

hi,
I think you need to calculate the probability that there will be no eruption for 25 years AND there will be exactly 1 eruption in the next 25 years.

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