 # Addition to 20 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.

## Introduction

Start with a few counting to 20 exercises. Ask students to count and then to explain their counting strategy. It is possible for example to count in groups of 5, 2, or 3. You then decompose numbers to 20 into groups of tens and the ones. For example 13 to 10 and 3.

## Instruction

Check that students are able to add to 20 using simplification by asking the following questions:
- 6+2= 8, 16+2 =?
- 4+3= 7, 14+3=?
- 1+4 = 5, Which total can you easily calculate?

## Quiz

Students first practice with an addition problem with visual support. They need to give the answer to both addition problems. Next, they solve without visual support, but they are given the answer to the addition problem made of ones. Finally they must solve both the ones and tens addition problem.

## Closing

Repeat why it is important to learn how to do this. It is useful because it speeds up calculation. If you know the total of ones (below ten), then you know the sum of the tens addition problem as well. Check that students have understood by doing two addition problems where students have visual support, and a few problems without visual support.

## Teaching tips

Students who have difficulty can be supported with MAB-blocks or other manipulatives like the rekenrek or money. Give them a dollar bill and a five dollar bill. They know that 1+5 is 6 dollars. Give them a 10 dollar bill and then they have 11 +5=16. Repeat this with other amounts. Emphasize that they should not recalculate the problem but simply use the total they already have but add ten.

## Instruction materials

MAB-blocks (tens and single blocks) 