Arithmetic mean is a concept which, although simple in form, is quite complicated to fully understand. The purpose of this study was to examine how experts understood arithmetic mean in order to provide articulations of their understandings. Additionally, the articulations of conceptions of arithmetic mean could give a research-based foundation to future studies done to examine how to develop understanding of arithmetic mean. Five participants, each with expertise with arithmetic mean, were interviewed to probe into how they were thinking of arithmetic mean. Analysis of the interviews led to...