This learning resource focuses on the foundations of multi-digit arithmetic, particularly aimed at enhancing students' abilities to solve addition and subtraction problems using standard algorithms and mental math strategies. The resource begins with an objective that outlines the expected outcomes: by the end of the learning session, students will accurately perform multi-digit calculations while explaining their thought processes. The guide emphasizes place value logic, illustrating the importance of vertical alignment of numbers and the procedures of regrouping in addition and borrowing in subtraction. Examples and exercises encourage students to apply these algorithms practically while also allowing them to explore mental math shortcuts for verification. Additionally, comparative strategy analyses are included to assess efficiency versus reliability in problem-solving. Reflection prompts guide students to think critically about their approaches, while diagnostic error analysis helps identify common misconceptions. Overall, this resource supports the development of robust arithmetic skills essential for further mathematical learning.