On the basis of examining the Mathematics and the Informatics curricula of the 7 th grade, this article delineates the researching process, from which the procedure of exploiting the interdisciplinary relationship between Mathematics and Informatics in teaching the solving methods of exercises on algebraic expressions with the assistance of Microsoft Excel is deduced and subsequently proposed and illustrated. The results are acquired via analysing and synthesizing theory as well as studying the reality of teaching and studying Mathematics and Informatics in secondary schools. The result has identified a number of similarities between the contents the Mathematics and the Informatics educational plans of the 7th grade together with the procedure of exploiting the Mathematics - Informatics interdisciplinary relationship in teaching about solving problems about algebraic expressions. By doing excercises, students are able to revise and consolidate mathematical and informatic knowledge while being more aware of the application of computer science in education and daily life.