BETADIST function
Returns the cumulative beta probability density function. The beta distribution is commonly used to study variation in the percentage of something across samples, such as the fraction of the day people spend watching television.
Syntax
BETADIST(x,alpha,beta,A,B)
X is the value between A and B at which to evaluate the function.
Alpha is a parameter of the distribution.
Beta is a parameter of the distribution.
A is an optional lower bound to the interval of x.
B is an optional upper bound to the interval of x.
Remarks

If any argument is nonnumeric, BETADIST returns the #VALUE! error value.

If alpha ≤ 0 or beta ≤ 0, BETADIST returns the #NUM! error value.

If x < A, x > B, or A = B, BETADIST returns the #NUM! error value.

If you omit values for A and B, BETADIST uses the standard cumulative beta distribution, so that A = 0 and B = 1.
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.
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.

