Contributing to a growing body of research on undergraduate students' quantitative reasoning, the study reported in this article used task-based interviews to investigate business calculus students' quantitative reasoning when solving two optimization tasks situated in the context of revenue and profit maximization. Analysis of verbal responses and work written by 12 pairs of students during the task-based interviews revealed that nearly all pairs of students created new quantities (e.g., diminishing marginal returns). Students used these new quantities to reason about relationships among computer sales, sales discount, and total revenue in a revenue maximization task. The creation of these quantities helped the students to solve the problem posed in the task. Ten pairs of students interpreted marginal cost as total cost and marginal revenue as total revenue in a profit maximization task. Implications for business calculus instruction and directions for future research are discussed.