This paper presents a simple extension of Rolle's Theorem. This extension allows determining the amount of numbers ξ in which f'(ξ ) = 0 in a given interval, using the characteristics of the function f in that interval. The extension has been proved, and the geometric interpretation has been presented. Illustrative examples have also been developed for each case that can be obtained by applying the extension. Finally, the study examines the relation of this theorem with the problem of multiple internal rates of return (IRR). i i