POISSONPDF.81 (Poisson Probability Density Function) freeware
by Daniel Bishop (danb2k@hotmail.com)
2000-10-09

This program evaluates the poissonpdf(lambda, x) function as used on the TI-83.  LAMBDA is the expected number of times an event will occur within a given time period.  This program calculates the probability P(X) that the even will occur X times during a time period of equal length.

Prgm_:POISSONP
:Disp "LAMBDA"
:Input L
:Disp "X"
:Input X
:L^X/e^L/X! -> P
:Disp "P(X)="
:Disp P

Example:
In a certain small town, an average of six babies are born each month.  What is the probability that exactly five children are born there this month?

Solve:
lamba=(6/month)(1 month)=6
X=5

Run program:
LAMDA
?6
X
?5
P(X)=
      .160623141