# 4. Add 10 and 100 mentally (FP)

teaches Common Core State Standards CCSS.Math.Content.2.NBT.A.2 http://corestandards.org/Math/Content/2/NBT/A/2
teaches Common Core State Standards CCSS.Math.Content.2.NBT.B.8 http://corestandards.org/Math/Content/2/NBT/B/8
teaches Common Core State Standards CCSS.Math.Practice.MP8 http://corestandards.org/Math/Practice/MP8

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Lesson objective: Relate skip counting to mentally adding ten and one hundred.

This lesson helps to build procedural skills with mentally adding ten and one hundred. An open number line is used here because it supports the mental math that students are experiencing. This work develops students' understanding that we can use skip counting to add or subtract because, when we count, we move along the number line.

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as students notice the repeated pattern when skip counting, and how this helps them mentally add or subtract numbers using numerical reasoning. Students have been working with hundreds charts, counting strips, and open number lines to build their understanding of mental addition.

Key vocabulary:

• decompose
• decrease
• open number line

Special materials needed:

• "Hip Hop to 500" Recording Sheet
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