We apply an advanced data visualization technique, "Sankey diagram," to explore how middle-school students (N = 343) solved problems in a game-based algebraic notation tool. The results indicate that there is a large variation in the types of students' strategies to solve the problems, with some approaches being more efficient than others. The findings suggest that Sankey diagrams can be used both in research and practice to unpack our understanding of variability in mathematical problem-solving. [This paper was published in: "Proceedings of the 15th International Conference of the Learning Sciences--ICLS 2021," 2021, pp. 887-888.]