This study examined if solving arithmetic problems hinders undergraduates' accuracy on algebra problems. The hypothesis was that solving arithmetic problems would hinder accuracy because it activates an operational view of equations, even in educated adults who have years of experience with algebra. In three experiments, undergraduates (N = 184) solved addition facts or participated in one of several control conditions. Those who solved addition facts were less likely to solve prealgebra equations (e.g., 6 + 8 +4 = 7 + __) correctly under speeded conditions. In a fourth experiment, the negative effects of solving arithmetic problems extended to undergraduates (N = 74) solving algebra problems with no time pressure. Taken together, results suggest that arithmetic activates knowledge that hinders performance on algebra problems. Thus, an operational view of equations, which is prevalent in children, does not seem to be revised or abandoned, even after years of experience with algebra.