Simply memorizing calculation methods can build 'calculation skills,' but it doesn't necessarily lead to true 'math ability.' Just as there are principles and methods behind calculation, each type of calculation has its own characteristics and relationships to other calculations. Children also need opportunities to apply calculations in practice and to develop number sense through them. With this in mind, this workbook is designed—based on sound mathematical reasoning—to help children explore each operation from multiple angles, enabling well-rounded, three-dimensional calculation training rather than one-dimensional practice. 1. (3-digit number) + (3-digit number) without carrying 2. (3-digit number) + (3-digit number) with one carry 3. (3-digit number) + (3-digit number) with two carries 4. The relationship between addition and subtraction 5. (3-digit number) - (3-digit number) without borrowing 6. (3-digit number) - (3-digit number) with one borrow 7. (3-digit number) - (3-digit number) with two borrows 8. Basics of division 9. Division within multiplication tables with no remainder 10. (2-digit number) × (1-digit number) without carrying 11. (2-digit number) × (1-digit number) with one carry 12. (2-digit number) × (1-digit number) with two carries