Wardani, Kartika Dyah, and Rully Charitas Indra Prahmana. “Learning Direct and Inverse Proportion Using Pen and Money for Slow-Leaners”. Indonesian Research Journal in Education |IRJE|, vol. 5, no. 1, Apr. 2021, pp. 63-84, doi:10.22437/irje.v5i1.10302.