In Excel 2010, the Binomdist function has been replaced by the Binom.Dist function, which has improved accuracy.
Although it has been replaced, the Binomdist function is still available in Excel 2010 (stored in the list of compatibility functions), to allow compatibility with earlier versions of Excel.
The Excel BINOMDIST function returns the Binomial Distribution probability of a specified number of successes out of a specified number of trials.
The format of the function is:
where the arguments are shown in the table below:
number_s    The number of successes that you want to calculate the probability for.  
trials    The number of independent trials that are to be done.  
probability_s    The probability of success in one trial.  
cumulative    A logical argument that specifies whether you want to calculate the cumulative distribution function or the probability mass function. This argument can have the value TRUE or FALSE, meaning:

Note that if decimal values are input for the number_s or trials arguments, these are truncated to integers by Excel.
+ Display Binomial Distribution Summary:
The Binomial Distribution is a statistical measure that is frequently used to indicate the probability of a specific number of successes occurring from a specific number of independent trials.
The following two forms are used:
The above chart on the right shows the Binomial Distribution Probability Mass Function for 100 tosses of a coin. The chart shows the probability that exactly x heads will be thrown from 100 tosses of a coin.
In the spreadsheets below, the Excel Binomdist function is used to evaluate this function for three different values of x.
Clearly, the probability of tossing a head on any one trial is 0.5 (or 50%), so this is input as the probability argument to the functions.
Formulas:  Results: 
The above chart on the right shows the Binomial Cumulative Distribution Function for 100 tosses of a coin. The chart shows the probability that at most x heads will be thrown from 100 tosses of a coin.
In the spreadsheets below, the Excel Binomdist function is used to evaluate the Cumulative Distribution for three different values of x.
Once again, the probability of tossing a head on any one trial is 0.5 (or 50%), so this is input as the probability_s argument.
Formulas:  Results: 
Further examples of the Excel Binomdist function can be found on the Microsoft Office website.
If you get an error from the Excel Binomdist Function, this is likely to be one of the following:
#NUM!    Occurs if either:

#VALUE!    Occurs if any of the number_s, trials, or probability_s arguments are nonnumeric. 