EXPONDIST function
Returns the exponential distribution. Use EXPONDIST to model the time between events, such as how long an automated bank teller takes to deliver cash. For example, you can use EXPONDIST to determine the probability that the process takes at most 1 minute.
Important This function has been replaced with one or more new functions that may provide improved accuracy and whose names better reflect their usage. This function is still available for compatibility with earlier versions of Excel. However, if backward compatibility is not required, you should consider using the new functions from now on, because they more accurately describe their functionality.
For more information about the new function, see EXPON.DIST function.
Syntax
EXPONDIST(x,lambda,cumulative)
The EXPONDIST function syntax has the following arguments:

X Required. The value of the function.

Lambda Required. The parameter value.

Cumulative Required. A logical value that indicates which form of the exponential function to provide. If cumulative is TRUE, EXPONDIST returns the cumulative distribution function; if FALSE, it returns the probability density function.
Remarks

If x or lambda is nonnumeric, EXPONDIST returns the #VALUE! error value.

If x < 0, EXPONDIST returns the #NUM! error value.

If lambda ≤ 0, EXPONDIST returns the #NUM! error value.

The equation for the probability density function is:

The equation for the cumulative distribution function is:
Example
The example may be easier to understand if you copy it to a blank worksheet.
How do I copy an example?

Select the example in this article.
Important Do not select the row or column headers.
Selecting an example from Help

Press CTRL+C.

In Excel, create a blank workbook or worksheet.

In the worksheet, select cell A1, and press CTRL+V.
Important For the example to work properly, you must paste it into cell A1 of the worksheet.

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.
After you copy the example to a blank worksheet, you can adapt it to suit your needs.

