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Next: Poisson random variable 11/2 Up: Special Distributions Previous: Geometric 11/3

Negative Binomial 11/3

This is the number of trials until r successes is obtained in a sequence of Bernouill(p) trials.


\begin{displaymath}P(X=k)=p \times \binom{k-1}{r-1} p^{r-1} q^{(k-r)}=
\binom{k-1}{r-1} p^{r} q^{(k-r)}\end{displaymath}

In fact the Geometric is the special case where r=1.

Susan Holmes