BINOMDIST function
In Excel 2010, several functions have been implemented with new algorithms for improved accuracy.
Read a blog post or try Office 365!
Returns the individual term binomial distribution probability. Use BINOMDIST in problems with a fixed number of tests or trials, when the outcomes of any trial are only success or failure, when trials are independent, and when the probability of success is constant throughout the experiment. For example, BINOMDIST can calculate the probability that two of the next three babies born are male.
Syntax
BINOMDIST(number_s,trials,probability_s,cumulative)
Number_s is the number of successes in trials.
Trials is the number of independent trials.
Probability_s is the probability of success on each trial.
Cumulative is a logical value that determines the form of the function. If cumulative is TRUE, then BINOMDIST returns the cumulative distribution function, which is the probability that there are at most number_s successes; if FALSE, it returns the probability mass function, which is the probability that there are number_s successes.
Remarks

Number_s and trials are truncated to integers.

If number_s, trials, or probability_s is nonnumeric, BINOMDIST returns the #VALUE! error value.

If number_s < 0 or number_s > trials, BINOMDIST returns the #NUM! error value.

If probability_s < 0 or probability_s > 1, BINOMDIST returns the #NUM! error value.

The binomial probability mass function is:
where:
is COMBIN(n,x).
The cumulative binomial distribution is:
Example
The example may be easier to understand if you copy it to a blank worksheet.
How to copy an example

Create a blank workbook or worksheet.

Select the example in the Help topic.
Note Do not select the row or column headers.
Figure 1: Selecting an example from Help

Press CTRL+C.

In the worksheet, select cell A1, and press CTRL+V.

To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.

