This work is related to the problem of the development of the most adequate method of qualitative evaluation of mathematical exercises solutions in the framework of studying economic and mathematical disciplines. The author gives his own classification of possible mistakes, indicates their external features, analyzes their causes, tries to rank them according to the severity level. The article consists of two parts, the first of which contains the classification itself in general form, and the second one - concrete examples and some statistical data, received by the author.