Exponential and Poisson distributions

If events E, E2, , Ek can occur with prohahilities P, P2, , Pr, respectively, the prohahility that events E, E2, , Er will occur Xi,X2,---,Xr times respectively is given hy the multinomial distrihution 

One can show (refer to statistics textbooks) that the Poisson distribution is a limiting case of the binomial distribution, Eq. 2.40 with N 00, p 0 but with Np =, a constant. 

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Probability distribution. A mathematical model which, for a range of values, associates a probability (or probability density) with a given value. Common examples are the Normal binomial, t, F, chi-square, exponential (or negative exponential) and Poisson distributions. 

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