Butngam, O., I. Srisombut, and D. Thotong. “The Study of Larning Outcomes and Problem Solving Skll Toward Grade Students Taught by Problem Based Learning”. Academic MCU Buriram Journal, vol. 2, no. 1, June 2017, pp. 74-82, https://so06.tci-thaijo.org/index.php/ambj/article/view/241617.