Problem-solving competence is one of the abilities as a primary objective of the national curriculum because this ability is required to face future challenges. On the other hand, the ability of students to solve linear programming problems is still low. Where to improve this competency needs a systematic effort. Therefore, this study aims to: 1) improve student problem solving, 2) measure the level of validity, effectiveness, and practicality of the SAS developed. The type of this research is Research and Development (R&D) by Thiagarajan, Semmel and Semmel Model. The instrument developed was a student activity sheet (SAS) based on the Krulik dan Rudnick problem-solving. Furthermore, to obtain data in this study using four types of instruments: 1) observation sheets, 2) questionnaires, 3) validation sheets and 4) essay test based on Krulik and Rudnick problem-solving. This research conducted in the mathematics education study program in class C and bilingual. The results of data analysis showed an increase in students’ problem-solving skills. Besides, the activity sheet has met the criteria of validity, practicality, and effectiveness.