This study examined adult students' informal knowledge of percent and its relationship to their computational skills. Sixty adults studying in urban and suburban adult education programs were interviewed to ascertain: (1) their ideas of the meanings of benchmark percents, 100%, 50%, and 25%, as they appear in advertising and media contexts; (2) their ability to use these percents in everyday mental math tasks; and (3) their visual representations of these percents. Students also completed written computational percent exercises. Students' responses were examined to determine the nature of their informal knowledge and skills, and a number of patterns were identified. The range and fragility of student responses and the diversity of knowledge gaps suggest the acquisition of isolated ideas but the absence of elaborated frameworks. (Author/MKR)