This learning resource focuses on flexible partitioning strategies for multi-digit addition and subtraction. It guides students through various methods to break down numbers into more manageable parts, encouraging them to explore unique ways to add or subtract numbers. The document includes warm-up exercises, worked examples, guided and independent practice problems, and metacognitive reflections, allowing students to assess the efficiency of different strategies. Through creative tasks, students also design their own problems to illustrate the effectiveness of flexible partitioning over traditional algorithms and examine real-world applications of these skills. Overall, the aim is to enhance students' mental math abilities by fostering a deeper understanding of number relationships and operation flexibility.