 Students learn to add millimetres and centimeters.

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## General

Students learn how they can add millimeters and centimeters together.

## Common core standard(s)

CCSS.Math.Content.4.MD.A.2

## Learning objective

Students will be able to add millimeters (mm) and centimeters (cm) together.

## Introduction

On the interactive whiteboard there are a few numbers that the students must convert to millimeters or centimeters.

## Instruction

To check whether students can add millimeters and centimeters together, you can ask the following questions:
- How do you add centimeters and millimeters together, when you have to give the answer in millimeters?
- How do you add centimeters and millimeters together, when you have to give the answer in centimeters?

## Quiz

Students first practice adding millimeters and centimeters, for which they get a visual aid. Then they practice adding for which they are only given the numbers and they make a story problem, which they must then solve.

## Closing

You discuss with the students again that it is important to be able to add millimeters and centimeters together, because that is how you can determine how much something is in total. Check if they know that they must first convert to the same length measurement by multiplying or dividing by 10. For this, use a few problems on the interactive whiteboard with paint splotches over the answers. Have the students solve the problems and drag the paint spot out of the way, to show what the correct answer is.

## Teaching tips

When students have difficulty with adding millimeters and centimeters, you can give them a diagram of the metric system, wherein you only have centimeters and millimeters with an arrow for ÷10 and an arrow for x10. Explain that you first have to convert. Then you can add the numbers together.

## Instruction materials

You may print out a diagram of the metric system. 