# Thread: Help with Poisson Distribution

1. ## Help with Poisson Distribution

Hi guys I got a question on the poisson distribution and never previously done stats at all.

It follows:

The mean count of a radioactive substance is 25 disintegrations per minute. Using the Poisson distribution, find the probability that, in a time of 12 seconds, there are-

i) No disintegrations

ii) More than 2 disintegrations

2. ## Re: Help with Poisson Distribution

Originally Posted by mathsforumuser
Hi guys I got a question on the poisson distribution and never previously done stats at all.

It follows:

The mean count of a radioactive substance is 25 disintegrations per minute. Using the Poisson distribution, find the probability that, in a time of 12 seconds, there are-

i) No disintegrations
ii) More than 2 disintegrations
If you've never done stats, why do you have to answer this question?

As the mean count is 25 dpm this specifies the distribution parameter $\lambda=25$

i) is just the Cumulative distribution function (CDF) of the specified Poisson distribution evaluated at 0.

ii) is 1 - CDF(2)

you can find the CDF on wiki or by integrating the PDF of the Poisson distribution.