T. Namgyal and K. Kongmanus, “Effectiveness of a Mathematics Instructional Package on Pólya’s Steps Including Video Clips to Enhance Problem Solving Abilities of 6th Grade Students in Bhutan”, IJET, vol. 7, no. 4.38, pp. 965–969, Dec. 2018, doi: 10.14419/ijet.v7i4.38.27618.