There are three main forms of problems in mathematics textbooks in primary schools in Viet Nam: single problems, complex problems and typical problems. Among them, the typical problem is a problem that has a fixed solution. Normally, if students identify typical problems correctly, they will address them correctly. In this study, we only focus on one of typical problems “finding two numbers if their sum and their ratio are known” in Mathematics 4. It is the aim to examine the students’ capacity to solve the above form of problem and find out their mistakes made in the process of solving the problem. 92 primary school students participated in the research and they had to address two problems related to “finding two numbers if their sum and their ratio are known”. A detailed content analysis was used carefully. The findings showed that most students succeeded in solving the given problems, but they also committed some errors in their solutions.