 # Addition to 100 making ten

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## General

Students learn to add to 100 making ten.

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

## Relevance

Discuss with students that it is important to be able to add to 100 to be able to determine how many you have together.

## Introduction

Show the money amount on the interactive whiteboard and say that it must be added to to total 40. Students must determine how many more dollars are needed. Repeat this exercise with the stamps. Then ask students to decompose the given number. Ask students to write their answers and hold up their paper to check their answers. Erase the grey box to check the answer.

## Development

Check that students can add to 100 making ten by asking the following questions:
- What do you look at when you want to solve a story problem?
- How do you calculate 23+7 and 48==70?

## Guided practice

Students start by adding with visual support of a number line. They then must determine what the missing addend is, and finally students are asked to solve a story problem.

## Closing

Discuss with students that it is important to be able to add to 100, so you can determine how much you have in total. Show a number line on the interactive whiteboard and ask students to discuss in pairs how they would solve the addition problem. As a class discuss which steps you can take on the number line to solve the problem. Then ask students if they can fill in the blanks. Give students time to discuss and determine the answer and then ask a student in class for the answer. Ask them how they reached that total- to explain their thinking. Show the answer to check their work.

## Teaching tips

Students who have difficulty adding to 100 can use the number line as support. Make sure that they understand that they can take different steps (or jumps) on the number line. They can also be supported by practicing making ten, to make the next steps on the number line easier. 