Researchers who have carried out studies pertaining to mental computation and everyday mathematics point out that adults and children reason intuitively based upon experiences within specific contexts; they use invented strategies of their own to solve real-life problems. We draw upon research areas of mental computation and everyday mathematics to report on a study that investigated adults' use of mental mathematics in everyday settings. In this paper, we report on one adult's use of mental computation at work and highlight the role of context and context related parameters in his mental mathematical activities.