The main goals of the quantitative methods are clearly focused on the study of decision-making problems. The phases of the method are immediate. -The first phase, the formulation of the problem, plays a fundamental role, since it is on the basis of this that it is possible to judge which aspects should be analysed. -The second phase consists of the formulation of a mathematical model that describes the situation to be studied. A model is an abstraction or simplified representation of a part or segment of reality. Once the construction of the model has been completed, the selection of the specific criterion for evaluating the alternatives is addressed.