## 2.NBT.B.7

## Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.

31 Lesson(s)

#### Students often think that subtraction is simply “take away.” The goal of this lesson is to allow students to see the comparison (difference) between two numbers.

#### This lesson builds a foundation for adding larger numbers which is supported by the Common Core standards for second grade..

#### To help students develop fluency skills with adding and subtracting numbers within 100. A variety of strategies need to be presented to encourage students to think mathematically.

#### This lessons starts with a concrete representation of a change unknown problem and then pushes students to think abstractly and develop number sentences to solve change unknown word problems.

#### The Common Core standards expect addition and subtraction fluency with one and two digit numbers. Students need to develop efficient fluency strategies.

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#### Students use place value blocks to accurately subtract across zeros.

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#### Students develop their own strategies for solving two-step word problems.

#### Students identify, use, and share strategies for adding three-digit numbers that require regrouping.

#### Students identify, develop, use, and share their own strategies for solving change unknown word problems.

#### Understanding subtraction is as key to Common Core Standards as is understanding addition and it is usually much harder for students to grasp.

#### Being able to add and subtract with 10 and 100 is a Common Core skill expected of second grade students.

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