De La Salle Series: Arithmetics: Primary, LRC-20C4-13, Volume: 1. Lasallian Research Collection.
De La Salle Series: Arithmetics: Primary, LRC-20C4-13, Volume: 1. Lasallian Research Collection. https://archivesspace.manhattan.edu/repositories/5/resources/1679 Accessed January 27, 2021.