Priambada, Miko, Hardi Suyitno, and St. Budi Waluya. 2018. “Development of Mathematics Learning Tools of Group Investigation (GI) Model With Characters Contain to Increase Critical Thinking Ability”. Journal of Primary Education 8 (3), 323-30. https://journal.unnes.ac.id/sju/jpe/article/view/27788.