Lesson plan

8. Three-digit subtraction as a missing addend (C)

teaches Common Core State Standards CCSS.Math.Content.2.NBT.B.7 http://corestandards.org/Math/Content/2/NBT/B/7
teaches Common Core State Standards CCSS.Math.Content.2.NBT.B.9 http://corestandards.org/Math/Content/2/NBT/B/9
teaches Common Core State Standards CCSS.Math.Practice.MP1 http://corestandards.org/Math/Practice/MP1
teaches Common Core State Standards CCSS.Math.Practice.MP8 http://corestandards.org/Math/Practice/MP8
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Lesson objective: Understand and solve three-digit subtraction problems, with regrouping, as missing addend problems.

Students bring prior knowledge of adding and subtracting three-digit numbers from 2.NBT.B.9. This prior knowledge is extended to solving missing addend problems using a variety of addition or subtraction strategies. A conceptual challenge students may encounter is understanding the relationship between addition and subtraction.

The concept is developed through work with tape diagrams, which helps students see parts of a whole to support them in the understanding that subtraction problems help us find a missing part of the whole.

This work helps students deepen their understanding of operations because the relationship between addition and subraction can be used as a strategy to solve problems.

Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they find a missing addend by exploring both addition and subtraction strategies.  Tape models support students' understanding of subtraction problems as missing addend problems.

Key vocabulary:

  • addend
  • base ten blocks
  • decompose
  • digit
  • equivalent
  • hundreds
  • number line
  • ones
  • place value
  • regroup
  • tape diagram
  • tens