Mulyanto, Heri, Gunarhadi Gunarhadi, and Mintasih Indriayu. 2018. “THE EFFECT OF PROBLEM BASED LEARNING MODEL ON STUDENT MATHEMATICS LEARNING OUTCOMES VIEWED FROM CRITICAL THINKING SKILLS”. International Online Journal of Education and Teaching 5 (3):553-63. https://www.iojet.org/index.php/IOJET/article/view/392.