Adding cm and m

General

Students learn how they can add centimeters and meters together.

Standards

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

Learning objective

Students will be able to add centimeters (cm) and meters (m) together.

Introduction

Several numbers are shown on the interactive whiteboard in centimeters or meters. The students must choose which number is larger for each problem. Circle the correct answer.

Instruction

Ask the students if they know how many centimeters there are in one meter. Then you measure the height of one of the students. Say that the student is 1 meter and ... centimeters. You can also add this up together to know how many centimeters the student is. To do this, you have to know how many centimeters are in 1 meter. Then you can add the centimeters together. Using a visual aid, show how you can add meters and centimeters together. Explain that you can add meters and centimeters by first converting meters to centimeters, then adding them together. Have the students practice on their own using a visual aid. Afterwards you explain again how you can add meters and centimeters together by first converting meters to centimeters. To do this you take two jumps to the right, so you multiply by 100. Discuss a few problems with the class. Then the students must solve a problem, for which they can choose from a few possible answers or determine the answer by themselves. Next you explain that you can also convert to meters. You take two jumps to the left, so you divide by 100. Have the students solve a few problems on their own. Afterwards, you discuss addition of meters and centimeters in the form of a story problem. The story problem can be either a multiplication or a division problem. Have the students solve a story problem on their own.

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

Quiz

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

Closing

You discuss with the students again that it is important to be able to add centimeters and meters together, so that you can determine how long something is in total. Check whether they know that they must first convert to the same measurement by multiplying or dividing by 100. Do this with the starting number on the interactive whiteboard. State how much they need to add to it. The students must give the answer in centimeters. Get rid of the box to show what the correct answer is. Then they must continue calculating with the new number. Have the students do this again, but then they must give the answer in meters.

Teaching tips

When students have difficulty with adding centimeters and meters together, you can give them an outline of the metric system, on which you only have centimeters and meters with an arrow for ÷100 and another for x100. Explain that you first have to convert. Then you can add the numbers together.