Siragih, Hermita Tri Indah, et al. “Analysis of Students’ Difficulties in Understanding the Concept of Summation in Grade II Students of UPTD State Elementary School 124407 Pematangsiantar”. JPG: Jurnal Pendidikan Guru, vol. 7, no. 4, Oct. 2026, pp. 711-8, doi:10.32832/jpg.v7i4.25450.