What key concept is involved in Tier 2's 'complements of 10'?

The key concept of 'complements of 10' revolves around using strategies that help visualize and understand addition better. When students learn about complements of 10, they grasp how certain pairs of numbers can combine to make 10. For example, knowing that 2 and 8, or 4 and 6, are complements of 10 allows students to quickly and effectively solve addition problems, as they can mentally group numbers that round up to 10 and then add any remaining amounts.

Using puzzle-like strategies enhances students' ability to see the relationship between numbers, which aids in developing their overall mathematical thinking. This visual approach not only makes learning addition more engaging but also strengthens their understanding of number concepts as they recognize patterns and relationships.

The other aspects, such as finger counting, mental math subtraction, and rapid calculations without tools, do not encapsulate the primary idea of complements of 10 as effectively as visual strategies do. Instead, they focus more on individual skills rather than the connected understanding of numbers that complements of 10 promotes.