In this paper a novel modelling and solving method has been developed to address the so-called resource constrained project scheduling problem (RCPSP) where project tasks have multiple modes and also the preemption of activities are allowed. To solve this NP-hard problem. a new general optimization via simulation (OvS) approach has been developed which is the main contribution of the ... https://parisnaturalfoodes.shop/product-category/clarifying-shampoo/