According to the results obtained in the research Project: (Didactics for Teaching the Probability in Middle Education”, presented as a requirement to get the academic title of MA: in Mathematics Teaching, offered by the Universidad Tecnologica de Pereira, one of the topics that must be taught at that level of education, and which presents a high difficulty degree to be understood by the students, is the Calculus of the Conditional Probability. In this sense, a method that allows facilitating the teaching-learning process on this topic, to young people who are passing from concrete to formal thought is introduced. The methodology consists on reducing the sample space in one and two variables, taking as a starter point the conjunctive and marginal probability for the bi-varied case, in order to explain the way to conceptualize it through examples.