Returns the inverse of the cumulative beta probability density function. That is, if probability = BETADIST(x,...), then BETAINV(probability,...) = x. The cumulative beta distribution can be used in project planning to model probable completion times given an expected completion time and variability.

Parameters :

	Probability	is a probability associated with the beta distribution.
	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. (=0)
	B	is an optional upper bound to the interval of x.(=1)