Kummod A, Art-in S. The Development of Mathematics Problem Solving Ability for Grade 12 Students Through Open Approach with Polya’s Problem Solving Process. JILS [internet]. 2019 Sep. 18 [cited 2026 Sep. 14];13(2):125-3. available from: https://so02.tci-thaijo.org/index.php/EDGKKUJ/article/view/216861