This study investigated the relationships among the symbolic representation of problems given to students to solve, the mental representations they use to solve the problems, and the accuracy of their solutions. Twenty eleventh-grade science students were asked to think aloud as they solved problems on the ideal gas laws. The problems were presented in five different symbolic forms (words, diagrams, tables, numbers, and graphs) and required either a numerical or a qualitative response. The results showed that students translated from the symbolic form of the problem to a symbolic representation corresponding to the response required (quantitative or qualitative). The accuracy of students' mental representations and responses depended in part on students' instructional histories. The implications of these findings for further research and practice in instruction and testing are discussed. (Author)