2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/17347A simple model of a buying-selling cycle is proposed. The model comprises two moves: a rational buying and a random selling. The notion of a profit intensity is introduced. Supply and demand curves and geometrical interpretation are discussed in this context.11 pages, LaTeX, no special macrosCondensed Mattertext