Which area of mathematics focuses on ratios and proportions?

The focus on ratios and proportions falls primarily under the category of algebraic concepts. Ratios express a relationship between two quantities, typically as a fraction, and proportions state that two ratios are equal. In algebra, these concepts are crucial for solving equations and understanding relationships between variables.

Arithmetic operations might involve the basic computation needed to manipulate these ratios, but they do not encompass the broader scope of understanding and using ratios and proportions as algebra does. Geometric concepts may use ratios, especially in similar figures, but they do not primarily focus on them. Calculus principles involve higher-level mathematics that is not fundamentally concerned with ratios and proportions in the same way algebra is. Thus, algebraic concepts provide the best framework for understanding and working with ratios and proportions, making it the correct answer.