Excel Function POISSON

POISSON(x, mean, cumulative)

Returns the probability of getting less than or equal to a particular value in a poisson distribution.

x	The number of events.
mean	The expected numeric value.
cumulative	The type of function to use True = cumulative probability function False = probability mass function

Remarks

* POISSON.DIST was added in Excel 2010 to replace this function.
* The Poisson distribution is a discrete distribution.
* A common application of the Poisson distribution is predicting the number of events over a specific time, such as the number of cars arriving at a toll plaza in 1 minute.
* If "x" is not an integer, it is truncated.
* If "x" is not numeric, then #VALUE! is returned.
* If "mean" is not numeric, then #VALUE! is returned.
* If "mean" = 0, then #NUM! is returned.
* If "x" < 0, then #NUM! is returned.
* If "x" = 0, then
* In Excel 2010 the accuracy of this function was improved.
* For the Microsoft documentation refer to support.office.com

	A
1	=POISSON(2,5,FALSE) = 0.084
2	=POISSON(2,5,TRUE) = 0.125
3	=POISSON(2,2,1) = 0.677
4	=POISSON(-2,2,1) = #NUM!