The formula used with Bernoulli
trials computes the binomial probability of obtaining
exactly "r" events in "n" trials:

n = number of trials
r = number of specific events you wish to
obtain
p = probability that the event will occur
q = probability that the event will not
occur
(q = 1  p, the
complement of the event) 
If you enter the formula directly on
the home screen, be careful
to use parentheses when entering the
exponent of n  r (or do the subtraction mentally
and enter your calculation).
Consider a problem
where
n = 6, r = 3, and p = 50%
(so, p = .5 and q =
.5, where q = 1  p)
(Remember, the function
nCr is
found under
MATH
→ PRB #3 nCr
and requires that the first value, n, be entered
before the function is called.) 

The easiest way to utilize the calculator to solve this formula is
to engage the binompdf function:
binompdf( 
binomial distribution probability density
function, which is:
where
(When using this builtin function there is no need to
type in the formula  YEA!!) 
Consider, again, a problem where
n = 6, r = 3, and p = 50%
(Remember, the function
binompdf is found under
DISTR (2nd VARS), arrow down to #0 binompdf
and the parameters are:
binompdf (number of trials,
probability of occurrence, number of specific events) 

