 Addition with decimal numbers with 3 decimal places

# Addition with decimal numbers with 3 decimal places

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## General

Students learn to add decimal numbers with 3 decimal places. They also learn to determine which numbers are required for a story problem.

6.NS.B.3

## Relevance

Discuss with students that it is important for them to be able to add decimal numbers with 3 decimal places, so they can determine totals of decimal numbers. You can also use it to calculate how many points a jury awarded someone.

## Introduction

Students practice by placing decimal numbers on the number line. They draw a line from the decimal number to where it belongs on the number line. Then they practice with the format of decimal numbers. Have them complete the decimal place number chart. Erase the grey boxes to check their answers.

## Development

Using the number line, explain how to add decimal numbers with 3 decimal places. Show that you leave the first addend whole (5.725) and that you split the second addend (2.192 into 2 and 0.192. Then use the number line to add 2 more. Then add the 0.192. Next show students a second addition option. That is that they split both addends into numbers before and numbers after the decimal point. That means for 5.725 + 2.192 you get 5+2 and 0.725 + 0.192. Calculate the totals and then add the two totals together to find the total. Check that students are able to calculate the totals of decimal numbers with three decimals with the following exercises. Emphasize that they should use the method they like best for calculation. Students are then given a problem in story form. Use the story with paint to discuss the steps they need to take to solve a story problem, and then have the students practice solving a story problem. Ask them to name the steps they take to solve the story problem.

Check that students are able to add decimal numbers with 3 decimal places by asking the following questions:
- What are the methods you can use to solve adding decimal numbers with 3 decimal places?
- Which method do you like best?
- How do you solve a story problem?
- What are the steps to solve a story problem?

## Guided practice

Students first practice adding simple addition problems with decimal numbers with 3 decimal places, and then are given more challening addition problems. They are then given story problems to solve.

## Closing

Discuss with students that it is important to be able to add decimal numbers with 3 decimal pints, so you can calculate decimal number totals. Check that students know which methods they can use to calculate the total of decimal number addition problems. Have students explain how to solve a story problem. Give a few addition problems to check that students have understood how to solve the addition problems. Have them explain the method they chose and why they selected it. Then have them do a story problem.

## Teaching tips

Students who have difficulty with adding decimal numbers with 3 decimal places should first practice setting decimal numbers on the number line. Give students a decimal number with 3 decimal places and have them add 0.001 each time. Also practice problems in which they jump from 0.009 to 0.010 and such.

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