The unit fraction is the basis of the fraction concept and has a role of starting point for understanding the fraction concept. In this study, in terms of the importance of the unit fraction, the teaching methods of the fraction based on the unit fraction were explored. First, it was examined the emerging contexts of the fraction concept and the diversity of its meanings. Second, it was investigated the contents of the unit fraction in Korean and CCSSM's curriculum and textbooks. Lastly, I suggested the teaching methods using the unit fraction in terms of the introduction of fraction, fractional operations, and teaching of problem solving based on the unit fraction.

The center of gravity of a triangle is the center of a physical shape. This is the content in the second grade of middle school, 'The Use of Similarity'. Unlike the cases of circumcenter and incenter, which are easily recognized visually, it is not easy for teachers to guide students with the visual meaning of center of gravity. According to the survey results, students, regardless of academic achievement, grade, and major, perceived the center of gravity of various plane figure as the center of their shape within a limited area through visual judgment. With reference to the results and contents of this process, it is hoped that the point of the three medians is meaningful not only in argumentative definition that the intersection of the triple line is the center of gravity of the triangle, but also in the center of a figure.