Lesson plan

Solve addition and subtraction problems within 100 by using a length model and number line

teaches Common Core State Standards CCSS.Math.Content.2.MD.B.5 http://corestandards.org/Math/Content/2/MD/B/5
teaches Common Core State Standards CCSS.Math.Content.2.MD.B.6 http://corestandards.org/Math/Content/2/MD/B/6
teaches Common Core State Standards CCSS.Math.Practice.MP4 http://corestandards.org/Math/Practice/MP4
teaches Common Core State Standards CCSS.Math.Practice.MP7 http://corestandards.org/Math/Practice/MP7

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Big Ideas: We can add two lengths to get the length of the whole. We can subtract one length from another to find the difference in lengths. When two numbers are added together the order does not matter. The sum will be the same. When we add two or more numbers in any order we get the same sum. Order does not matter. This lesson builds on students' work of addition and related subtraction combinations within 20. Students are asked to solve several number puzzles involving finding the sum of two or more lengths and finding the difference between lengths to reinforce the big ideas. Students also have opportunities to practice addition and subtraction by choosing two trains to find the sum or difference. Students are encouraged to show their thinking with a length model, number line model, and addition and subtraction strategies that make sense to them. The addition number puzzles build on the big idea that order does not matter when we add two or more numbers. Vocabulary: compare, difference, combine, sum, total, addition, subtraction, number line Special Materials: math tools that can be organized into tens and ones class number line (optional) student number lines (optional)