The basic concepts that students have in mathematics need more attention because these basic concepts will have an influence in understanding other mathematical concepts at a higher level. One of the basic concepts in mathematics is the concept of fractions. The concept of fractions was chosen in this study because of several things, first, fractions are an important concept in mathematics, second, the concept of fractions is one of the first abstract concepts that students learn in mathematics, and third, there are still many students who make mistakes when working on problems related to fractions. This study used a qualitative method with a case study design and involved 31 students of grade 7 junior high school in Bandung district. The triangulation technique used in this study is observation, tests, and interviews. The results showed that three were learning obstacle that was found by students including, 1) Ontogenic obstacle which is psychological, where students had weak motivation when learning the concept of fractions, 2) didactical obstacle, where students only gathered on procedural knowledge when learning the concept of fraction, and 3) epistemological obstacle, where there is a limited understanding of students regarding the operations of counting integers with fractions.

Geometry is one of the subjects in mathematics school that is important to learn, because through geometry, almost every daily problem can be solved. However, the achievements of Indonesian students in the field of geometry are still relatively low. This study aims to identify the possibility of students' learning obstacles in one area of geometry, which is circle subject. The method used in this study was qualitative research method with survey-based research design, involved 30 eight-grade students from a junior high school in Bandung. The data were collected by triangulation method using an instrument test consisting of tests of students mathematical comprehension ability that is related to circle subject, and the non-test instruments used consist of collection of observations, guidelines for student interviews, and study documents. Results showed that there were identified any types of learning obstacle caused by epistemological obstacle among others (1) learning obstacle related to the concept of sector caused by an error in the perspective of students, (2) learning obstacle related to the form of geometrical representation from the central angle of the circle caused by the student's limited knowledge of the central angle and chord of the circle. In addition, also found types of learning obstacle caused by didactical obstacle, among others (1) learning obstacle related to communication skills in presenting the definition of sector concept caused by not creating discussion and presentation activities when learning takes place, and (2) learning obstacle related the concept of the relationship between the diameter with chord of the circle caused by the presentation of material that is less detailed either provided by the teacher or presented in the source book used.

The decision support system is a system that can provide problem-solving abilities and communication skills for problems with semi-structured and unstructured conditions, such as determining which employees deserve a bonus. The decision-making process is a frequent occurrence and is at the core of activities at PT Perta Arun Gas, one of which is to determine bonuses for employees by calculating the average value of criteria for each employee, not counting the values of related criteria. The system designed is a decision-making system to determine employees who get bonuses using the Analytic Network Process (ANP) method, this ANP method can calculate the related criteria values. ANP is a method that accommodates the relationship between criteria and alternatives. The criteria used are, professional at work, politeness (behavior), presence, loyalty (a sense of ownership of employees towards the company), responsibility, cleanliness tidiness, and discipline. The test results indicate that this system can solve the problem of determining the distribution of bonuses to employees so that it can help in selecting employees who receive the bonus.