This paper is the outcome of a collaborative endeavour between mathematics and science educators where the insight from each field mutually informed one another. Specifically, building on the knowledge base from mathematics education research, this study analyses the ways in which percent is interpreted by first year university students in general chemistry. The content analysis of the chemistry problems reveals six categories of situations where percent is distinctly used. Within each category, we unfold the mathematical structure of the chemistry problems to feature the inherent complexity in setting the functional relationship among quantities. Our analysis also highlights how percent is used as an intensive quantity involving an implicit referent that conceals its interpretation. The strategies used by the students included the unitary analysis method, the equation method and the proportion method. Furthermore, percent was commonly interpreted as a fraction, ratio and operator. Although inadequate conceptual knowledge of chemistry explained some of the errors observed in the percent problems, the procedural meaning attached to percent in terms of its operator interpretation tend to be equally influential. Importantly, our study highlights how the knowledge base from mathematics and chemistry education can productively be used to further our understanding of the mathematical knowledge for learning chemistry.