Abstract :
This study was conducted to determine students mistakes in solving math problems the subject of aritmatica social in terms of the ability of students. Research was conducted is students of class VII F SMPK St Yoseph Naikoten 2 Kupang, totaling 3 student. The data used in this study was obtained through the test questions in advance and the interviewing process by using sample of three students are students with high ability, students with moderate ability and low ability students. Result from this study is the type of eror that made students include misconceptions, mistakes and miscalculations understand about the data. In general, the most prominent mistakes do learners was a miscaculation and error to understand the matter. Based on the results of the analysis can be seen that the most prominent mistakes do learners was a miscalculation and error to munderstand the matter, this was due to lack of understanding of the material and the lack of rigor in the students work on the problems.