# 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

## You have saved this lesson!

Here's where you can access your saved items.

Dismiss

Card of

You'll gain access to interventions, extensions, task implementation guides, and more for this lesson.

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:

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

Related content