Sari, Malda, and Edy Surya. 2017. “Improving the Learning Outcomes of Students Using Numbered Heads Together Model in the Subjects of Mathematics”. International Journal of Sciences: Basic and Applied Research (IJSBAR) 33 (3):311-19. https://www.gssrr.org/index.php/JournalOfBasicAndApplied/article/view/7558.