MENINGATKAN KEMAMPUAN PEMECAHAN MASALAH MATEMATIS MELALUI MODEL PROBLEM BASED LEARNING: IMPROVING MATHEMATICAL PROBLEM SOLVING ABILITY THROUGH THE PROBLEM BASED LEARNING MODEL. Abacus: Acad. J. Math. Learn. Educ. 2020;1(1):25-37. doi:10.59605/abacus.v1i1.383