Binomial Distribution
The best web site I found for seeing how the binomial distribution
responds to changes in p and n
is here
You can even use it to do your homework, because it calculates the
probability between any two limits.
Poisson Distribution
There is a Poisson CDF (Cumulative Density Function) calculator
which can be used instead of the tables. It is a little hokey, but it seems
to work. You have 3 boxes to put two numbers. The intensity is the mean
lambda, the probability is the value that you expect that fraction (e.g.0.95)
to be smaller than, and the X value is the cutoff value. If you want to
find the X value you must put a single question mark in that box. You can
solve for any one of the three (X, probability, or intensity lambda).
All Distributions
The most general calculator
I found can give you the probability, given distribution parameter(s) that
the sample is between any chosen values. The down side of this is that
it does not go both ways (i.e. allow you to figure out the cutoff value
for a given probability). Also, its control is a bit funky, necessitating
use of a check to include a boundary (and you have to reclick the check
when you change a distribution parameter). Still, it has every distribution
we will ever use in this class except the F distribution (late in the quarter).
It can be used for the binomial, Poisson and geometric distributions.