Abstract: The present study was carried out to investigate Goyal`s model (1985) and Teng`s model (2002) using the algebraic method to determine the optimal cycle time under delay payments. This paper provides algebraic approach that must be considered as a pedagogical advantage for explaining the inventory concept to students that lack knowledge of derivatives. This algebraic approach could therefore be used easily to introduce the basic inventory theories to younger students who lack the knowledge of calculus.