A Yun, Qurrota. 2018. “Improving Students Activity and Students Learning Outcomes by Using NHT (Numbered Heads Together) With PBI (Problem Based Instruction)”. Jurnal Axioma : Jurnal Matematika Dan Pembelajaran 3 (1):76-82. https://ejurnal.uij.ac.id/index.php/AXI/article/view/311.