This tool lets you calculate the probability that a random
variable X is in a specified range, for a variety of probability
distributions for X: the normal
distribution, the binomial
distribution with parameters *n* and *p*, the
chi-square
distribution,
the exponential distribution,
the geometric
distribution, the
hypergeometric distribution,
the negative
binomial distribution,
the
Poisson distribution, and
Student's *t*-distribution.

## Description of Applet Controls

The first choice box lets you select a
probability distribution. Depending on the distribution you
select, text areas will appear for you to enter the values of the
parameters of the distribution. Parameters that are probabilities
(*e.g.*, the chance of success in each trial for a
binomial distribution) can be entered either as decimal numbers
between 0 and 1, or as percentages. If you enter a probability as
a percentage, be sure to include the percent sign (%) after the
number.

The check boxes and corresponding text entry areas
let you constrain the range of values for which to find the
probability. If a box is not checked, there is no constraint in
that direction. For example if the box in front of >= is not
checked, the lower limit of the range of values for which the
probability is calculated is minus infinity; if the box in front
of <= is not checked, the upper limit of the range of values
for which the probability is calculated is infinity. When a box
is checked, the value in the corresponding text area limits the
range of possibilities for which the probability is calculated.