Amrina, Z., R. Desfitri, F. Zuzano, Y. Wahyuni, and H. Hidayati. “Development of Problem-Based Mathematic Learning Model to Increase Students’ Competence”. KnE Social Sciences, Vol. 3, no. 15, Mar. 2019, pp. 222–233, doi:10.18502/kss.v3i15.4369.