Some current models of mathematical cognition (Dehaene, 1992; Campbell & Clark, 1992) make strong claims about the code in which arithmetical operations are solved, basing themselves on how these operations were originally acquired or are most frequently employed. However, data on acquisition and use are often derived from anecdotic reports and no systematic figures have ever been collected. In this study a questionnaire was devised to investigate how participants learned multiplication tables, as well as the code in which one-digit and multi-digit operations are usually solved. The questionnaire was administered to two groups of university students, one Spanish (Study 1) and the other Belgian (Study 2). The results show that multiplication tables are mainly learnt by oral rehearsal, but adults solve multiplications more frequently by visualizing Arabic digits. This is also their preferred code for calculating additions, subtractions, and divisions. The preference for the Arabic code increases when subjects have to solve multidigit operations. (Contains 1 figure, 5 tables and 7 footnotes.)