BETAINV

BETAINV(probability, alpha, beta [,A] [,B])

Returns the inverse of the probability distribution function for a beta distribution.

probability	The probability associated with the distribution.
alpha	The parameter to the distribution.
beta	The parameter to the distribution.
A	(Optional) The lower bound to the interval of x.
B	(Optional) The upper bound to the interval of x.

REMARKS

* This function is only available for backwards compatibility and should not be used.
* BETA.INV was added in Excel 2010 to replace this function.
* The beta distribution is a continuous distribution
* If "probability" = 0, then #NUM! is returned.
* If "probability" > 1, then #NUM! is returned.
* If "alpha" = 0, then #NUM! is returned.
* If "beta" = 0, then #NUM! is returned.
* If "A" and "B" are left blank, then the standard cumulative beta distribution is used with A = 0 and B = 1.
* If "A" is left blank, then 0 is used.
* If "B" is left blank, then 1 is used.
* This function uses an iterative technique for calculating the function. Given a probability value, the function iterates until the result is accurate to within ±3x10-7.
* If any of the arguments are not numeric, then #VALUE! is returned.
* If the function does not converge after 100 iterations, then #N/A is returned.
* You can use the BETA.DIST to return the probability distribution function OR the cumulative distribution function for a beta distribution.
* For the Microsoft documentation refer to support.microsoft.com

	A
1	=BETAINV(0.685470581, 8, 10, 1, 3) = 2
2	=BETAINV(0.2, 1.5, 4, 1, 2) = 1.112
3	=BETAINV(0.5, 1, 2, 1, 2) = 1.293
4	=BETAINV(0.5, 1, -2, 1, 2) = #NUM!
5	=BETAINV(0, 8, 10, 1, 3) = #NUM!
6	=BETAINV(1, 8, 10, 1, 3) = #NUM!
7	=BETAINV("some text", 8, 10, 1, 3) = #VALUE!