Lesson objective: Add two three-digit numbers involving regrouping 10 ones to make a new ten, and/or 10 tens to make a new hundred.

This lesson provides an opportunity for students to apply their knowledge and understanding of three-digit addition with regrouping to a mathematical situation. Students are asked to validate or invalidate Dev's statement that the problem 496 + 404 only involves regrouping in the ones place.

Key Concept students will use:

- Addition strategies (such as regrouping) used with two-digit numbers can be used with three-digit numbers.

Skills students will use:

- Add numbers within 1,000 using knowledge of place value and properties of operations
- Add numbers within 100 using knowledge of place value (Grade 2, Unit 1)
- Represent three-digit numbers in different but equivalent ways (Grade 2, Unit 6)
- Understanding ten ones make a ten (Grade 1, Unit 1)

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they solve three-digit addition problems using previously learned strategies. Students will also apply regrouping strategies from two-digit addition to three-digit addition. Base ten blocks, number lines, and strategies related to place value will support students' understanding in this lesson.

**Key vocabulary: **

- base ten blocks
- compose
- decompose
- digit
- equivalent
- hundreds
- number line
- ones
- place value
- regroup
- tens