This textbook has been newly published to reflect the revised 2022 curriculum starting in 2024. 1. Ten problems solved with your mind are worth more than a hundred solved by hand alone. Calculation practice that only teaches computation methods can build 'calculation skills,' but not true 'math ability.' Just as there are principles and methods behind calculation, each calculation has its own properties and relationships to other calculations. Children also need to be able to apply calculations and develop number sense through them. To make this kind of well-rounded calculation training possible—rather than just one-dimensional practice—each operation is explored from multiple angles, with problems carefully designed based on sound mathematical reasoning. 2. It's not just the four basic operations, but math-infused calculation that builds a strong foundation for elementary, middle, and high school math. Because math is a subject that connects seamlessly from elementary through middle and high school, the concepts formed in elementary school directly affect learning in later years. While elementary concepts may seem simple, they connect to important ideas in middle and high school math, making it essential to learn calculation in a way that highlights its true mathematical meaning. This series also introduces mathematical rules from middle and high school at an elementary level, helping to anchor the overall structure of math learning from an early stage. 3. Thinking, solving, and feeling are what make math concepts stick. Calculation practice that focuses only on repetitive computation from start to finish can bore children and cause them to miss the mathematical meaning behind the numbers. This series creates a multi-dimensional learning structure that helps children understand the mathematical principles behind each calculation method, connecting practice to genuine conceptual understanding. The answer key also includes special notes explaining why each concept matters and how it connects to future learning in middle and high school. Contents: 1. Splitting and Combining Numbers 2. Addition with Sums up to 9 3. Subtraction of Single-Digit Numbers 4. The Relationship Between Addition and Subtraction 5. Splitting and Combining 10 6. Addition and Subtraction with 10 7. Consecutive Addition and Subtraction