# 12. Practicing finding the sum of problems with three and four two-digit addends (FP)

teaches Common Core State Standards CCSS.Math.Content.2.NBT.B.6 http://corestandards.org/Math/Content/2/NBT/B/6
teaches Common Core State Standards CCSS.Math.Practice.MP8 http://corestandards.org/Math/Practice/MP8

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Lesson objective: Add more than two addends that involve composing a new ten or hundred.

This lesson helps to build procedural skill with finding the sum of three and four two-digit addends. Composing a ten or hundred is used here because it enhances the understanding that numbers can be added in many different ways. This work develops students' understanding that the sum of an addition problem is the same no matter what order we add the numbers.

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they use the strategy of composing a new ten or hundred to solve addition problems with up to four addends.

Key vocabulary:

• compose
• decompose

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