This research aims to explore the use of ethnomathematics in revealing mathematical representations and in the formulation of a calculation system used in the "Marosok" trading tradition by the Minangkabau tribe in West Sumatra. Ethnomathematics studies ideas in various cultural activities practiced by ethnic, social, or professional groups. The tradition involves nonverbal communication, such as shaking hands with 'Marosok' or touching covered fingers to obtain price agreements in trading livestock. Therefore, this study was conducted using qualitative approaches and the ethnographic method via field notes, unstructured interviews, and documentation studies. The findings showed that mathematical representations of finger symbols and gestures in the "Marosok" Tradition contain basic numbers. These include half, one, two, two and a half, three, four, five, etc. with functions, such as addition and subtraction, which are used to obtain other numbers needed in livestock trading transactions using specific formulas.