Parent Support for K-5 Math

Third Grade Mathematics

Unit 1: Addition and Subtraction of Whole Numbers

What will your child learn in Unit 1?

In Unit 1, third graders will primarily work on 2- and 3-digit addition and subtraction problems. Students will use a variety of strategies to solve the problem. The solution methods range from using concrete models or drawings to strategies based on place value, meanings of operations, and number sense. To support the development of flexible addition and subtraction strategies, students will decompose and compose numbers. This will contribute to your child’s overall number sense. In addition, students will be guided on how to solve multi-digit problems using the standard algorithm. Students will understand why this method works and will apply this strategy to solve problems efficiently. Children go through different phases to quickly and accurately solve 2- and 3-digit addition and subtraction problems. Unit 1 will primarily focus on phases 2 and 3.

Furthermore, students will learn mental math strategies in this unit, such as rounding. They will also interpret data to solve addition and subtraction problems.

What math strategies will your child use in Unit 1?

There are a variety of strategies to help solve multi-digit addition and subtraction problems. The type of strategy depends on types of numbers used in the problem. The handout below gives an explanation of the different types of multi-digit addition and subtraction strategies.

Check out the videos below to see the math strategies in action. Most of the explanations are from students from our district. Thank you to the students for volunteering to explain their thinking!

• Partial Sums – Addition (Example 1)
• Partial Sums – Addition (Example 2)
• Open Number Line – Addition (Example 1)
• Open Number Line – Addition (Example 2)
• Compensation/Friendly Numbers – Addition (Example 1)
• Compensation/Friendly Numbers – Addition (Example 2)
• Open Number Line - Subtraction (Example 1)
• Open Number Line - Subtraction (Example 2)
• Open Number Line - Subtraction (Example 3)
• Removal – Subtraction (Example 1)
• Removal – Subtraction (Example 2)
• Breaking into Place Value – Subtraction (Example 1)
• Breaking into Place Value – Subtraction (Example 2)

How can you support your child at home to reinforce the concepts taught in Unit 1?

There are several ways to have your child practice the math concepts at home. Try the following activities:

• Give your child an addition or subtraction problem and have them solve it mentally and explain their thinking verbally.
• Have your child practice the number line strategy for addition and subtraction using an interactive open number line. Click the “i” on the bottom of the website for instructions on how to use it.
• Visit Base Blocks Subtraction to have your child practice the standard algorithm using place value blocks.
• Visit Thinking Blocks to have your child build models and solve addition and subtraction word problems.
• Have your child complete 3-Digit Addition Split to practice the Partial Sums strategy.
• Math Games for Home:Print the handouts to practice concepts through games.