This research aims to show the relationship that can be established between the understanding of the multiplicative structure given by the composition of natural multiplicative operators and the meaning that a student assigns to the muttiptication of fractions of the form 1/b when tryinq to solve sentence problems From some theoretical references {Dienes, 1972, Kieren, 1980, Llinares and Sánchez, 1988. Fandiño. 2009), we show that the way m which multipl»cation oí fractions is leamed and taught can be enhanced using Ihe natural multiplicativo oporators composition approach, Since, as will be sccn later. the solution of sentence problems involving multiplication ts achievcd by those students who are able to compose such operators. In this research. we used the case study method to describe and analyze student productions. considering three categories about reduction and composition of operators and multiplication of fractions of the form 1/b. Using the intra - subject and inter - subject analysis, we could determine that students who can establish the muttiplicative relationship between States can compose operators and solve problems about multiplication of fractions. beyond the application of the algorithm.