1. Suriasumantri J.S. 2010. Philosophy of Science: A Popular Introduction [Filsafat Ilmu: Sebuah Pengantar Populer]. Jakarta: Sinar Harapan.
2. Proportional reasoning: A review of the literature
3. Lamon S. Rational Numbers and Proportional Reasoning: Toward a Theoretical Framework for Research. In F. K. LesterJr. (Ed.), Second handbook of research on mathematics teaching and learning. Vol. 1, Information Age Publishing. Charlotte, NC; 2007. 629–667 p.
4. Kontogianni A, Tatsis K. Proportional Reasoning of Adult Students in a Second Chance School: The Subconstructs of Fractions. Adults Learn Math [Internet]. 2019;14(2):23–38. Available from: https://files.eric.ed.gov/fulltext/EJ1259506.pdf
5. Kilpatrick J, Swafford J, Findell B. Adding it up: Helping Children Learn Mathematics. Washington, DC: The National Academies Press; 2001.