Mathematics (2019) Grade(s): 2

MA19.2.14

Explain why addition and subtraction strategies work, using place value and the properties of operations.

COS Examples

Note: Explanations may be supported by drawings or objects.

Unpacked Content

Knowledge

Students know:
  • strategies for finding sums and differences.
  • physical (manipulative) models and pictorial models (place value blocks, lines and dots, bundles and sticks, etc.) for representing numbers using place value concepts.

Skills

Students are able to:
  • use logical reasoning, place value concepts and vocabulary, and properties of numbers and operations to justify strategies for finding sums and differences.

Understanding

Students understand that:
  • relationships between models of addition and subtraction problems and symbolic recordings of those models can be used to justify solutions and strategies.

Vocabulary

  • Properties of operations
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