 # Addition to 30 using simplification

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## General

Students learn that you can simplify the addition problem to tens and ones. If you know the total of the addition problem without the tens, you can calculate the addition problem with tens quickly.

2.OA.A.1
2.NBT.B.5

## Introduction

Start with some counting to 30 exercises. Have students count and then explain how they counted, for example with skip counting in 5s or 10s. Next, compose numbers to 30 to a tens and ones number. An example is 23 to 20 and 3.

## Instruction

Check that students understand addition to 30 using simplification by asking the following questions:
- 6+2= 8, 26+2 = ?
- 4+3= 7, 4+23 is 27, how do you know that?
- 4+5=9. Which addition problem can you now easily solve?

## Quiz

Students first solve an addition problem in which the first step problem is shown. Then they are asked to solve the first step as well as the actual problem. They are then challenged to make tens in their addition.

## Closing

Repeat why it is useful to learn how to simplify addition. It helps make calculations easier and faster. If you know the addition problem without tens, you can also do the problem with tens. Check that students have understood by doing a few problems in which they have visual support, and a few where they don't have visual support.

## Teaching tips

For students who have difficulty, they can be supported by using MAB blocks or other manipulatives like money or the rekenrek. Give them 1 dollar and 1 dollar. They know that the problem is 1+1 = 2. If you add a 10 dollar bill, it becomes 11+1= 12 dollars. Repeat with other amounts. Emphasize that they shouldn't recalculate but should just add 10 to the previous total.

## Instruction materials

MAB-blocks (tens and ones)

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