EXPONDIST
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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.
Syntax
EXPONDIST ( x , lambda , cumulative )
X is the value of the function.
Lambda is the parameter value.
Cumulative is 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 1
Formula 
Description (Result) 

=EXPONDIST(0.2,10,FALSE) 
Probability exponential distribution function (1.353353) 
Example 2
X 
Lambda 
Formula 
Description (Result) 

0.2 
10 
=EXPONDIST([X,][Lambda],TRUE) 
Cumulative exponential distribution function (0.864665) 