Consicler the Poisson distribution of the preceding problem.
(a) Show that it is properly normalized in tbe sense thst $\sum_{n=0}^{N} W_{n}=1$.
(The sum can be extended to infinity to an excellent spproximstion, since $W$. is negligibly small when $n \geq N .)$
(b) Use the Poisson distribution to calculate $\bar{n} .$
(c) Use the Poisson distribution to calculate $\left(\overline{\Delta n)^{2}}=\overline{(n-\bar{n})^{2}}\right.$.