# 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 when adding or subtracting one, two, or three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and if necessary, composes or decomposes tens and/or hundreds.

*TNCore Focus Standard

## Summary:

This skill asks students to add and subtract within 1000 using strategies based on properties of operations. Additionally, they should be able to model their strategies for solving such problems using manipulatives or drawings. Students should learn that when adding or subtracting one, two, or three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones, and if necessary, composes or decomposes tens and/or hundreds.
Also in grade 2, students will be developing fluency in addition and subtraction within 100. In grade 1, they developed the idea that when adding, one adds tens to tens and ones to ones, and the idea developed in standard 2.NBT.B.7 will be brought to fluency in Grade 3. Students will also learn to use strategies based on properties of operations as an alternative to the standard algorithm.

## Understanding the Standard:

• Provide students with a variety of opportunities for problem solving and deciding which strategy to use to add or subtract.
• Provide students with opportunities to write in their own words how they came to solve a particular problem. Doing so will encourage them to state the properties of operations in their own words and show mastery.
• Provide students with opportunities to use models or drawings to represent the strategy used to perform an operation (for example, adding ones to ones, tens to tens, and hundreds to hundreds).
• Provide students with carefully designed problems that will encourage them to be flexible in their problem-solving approaches, using the properties of operations.
• Encourage students to relate strategies to a written method, to use symbols, and to explain the reasoning behind the strategy used to perform and operation.

## Questions to Focus Instruction:

• Can students add or subtract one, two, or three-digit numbers, adding or subtracting hundreds and hundreds, tens and tens, ones and ones, sometimes composing or decomposing tens and or/hundreds?
• Are students able to recognize when regrouping will be necessary?
• Can students add or subtract within 1000 using strategies based on place value with the help of concrete models?
• Can students use symbols and relate their strategy to a written method? For example, if students use base-ten blocks to solve a subtraction problem, they should go a step further and figure out how to adapt their solution strategy into a written method (which may be the standard algorithm, a written method in which numbers are written in expanded form and subtracted place by place, or something else).
• Students should be able to see the connections between what is happening with manipulatives and/or drawings and what is happening in the written method. For example, exchanging a hundred block for ten tens is like subtracting one from the hundreds place in the standard algorithm and adding ten in the tens place.
• Can students justify the reasoning behind their strategy?

## Skills

Prior to: Students will add through 100 with one-digit and two-digit numbers. Students can properly choose whether to use addition or subtraction to solve a given word problem. Go to 1.NBT.C.4 to see previous skills in this progression.

At Grade Level: Students can fluently add and subtract within 1000 using concrete models or drawings and strategies based on place value and properties of operations. Students understand the concept of place value in adding and subtracting (i.e. adding/subtracting hundreds and hundreds, tens and tens, ones and ones), and can correctly identify when regrouping of ones, tens, and hundreds will be necessary in order to add and subtract.

Moving Beyond: Students will continue to add and subtract within 1000. Further, students will develop fluency in addition and subtraction within 1000 (3.NBT.A.2), and learn how to add and subtract numbers larger than 1000 (4.NBT.4).