# 2.6: Commutative Property of Addition with Decimals

**At Grade**Created by: CK-12

**Credit**: Tony Webster

**Source**: https://www.flickr.com/photos/diversey/17489073452/

**License**: CC BY-NC 3.0

Jeff’s dad works at an architectural firm in Boston. He has the same commute to work every day. First he drives 3.4 miles to the train station. Then he takes the train for 15.6 miles into the city. He’s lucky because the train station is right next to his office. To get home at the end of the day, Jeff’s dad does the reverse. How many miles does Jeff’s dad travel on his way home from work?

In this concept, you will learn to identify and use the commutative and associative properties of addition with decimals.

### Commutative Property of Addition

The **Commutative Property of Addition** states that when finding a sum, changing the order of the addends will not change their sum. In symbols, the commutative property of addition says that for numbers

Here is an example using simple whole numbers.

Show that

First, find

Next, find

Notice that both sums are 6.

The answer is that because both

The **Associative Property of Addition** states that when finding a sum, changing the way addends are grouped will not change their sum. In symbols, the associative property of addition says that for numbers

Here is an example using simple whole numbers.

Show that

First find

Next, find

Notice that both sums are 13.

The answer is that because both

Both the commutative property of addition and the associative property of addition can be useful in solving equations.

Here is an example.

Find the value of

First, notice that both sides of the equation are the sum of two values. Also, both sides of the equation include the number 71.321 as one of the terms.

By the commutative property of addition, the second term must also be the same on both sides of the equation.

The answer is

### Examples

#### Example 1

Earlier, you were given a problem about Jeff and his dad’s commute home from work. To get to work, Jeff’s dad drives for 3.4 miles and then takes the train for 15.6 miles. To get home, he does the reverse. Jeff wants to know how many miles his dad travels to get home.

First, figure out how many miles Jeff’s dad travels to get to work. You know that to get to work Jeff’s dad travels 3.4 miles plus 15.6 more miles.

This means Jeff’s dad travels 19 miles to get to work.

Now, to get home Jeff’s dad travels in reverse. By the commutative property of addition, you know that changing the order that you add two numbers won’t change the answer.

Therefore, Jeff’s dad must travel 19 miles to get home from work just like he travels 19 miles to get to work.

The answer is Jeff’s dad travels 19 miles to get home from work.

#### Example 2

Find the value of

First, notice that the right side of the equation has two addends grouped together. Use the associative property of addition to rewrite the right side of the equation by changing the way the addends are grouped.

Now, combine the terms in parentheses on the right side of the equation.

Next, notice that both sides of the equation now have two terms that are added together. Also, both sides of the equation have a 2.58 as one of the terms. This means the second terms on each side of the equation must be equal.

The answer is

#### Example 3

Identify which property is shown below.

First, notice that both sides of the equation have the same two addends, but the order has been changed. This is an example of the commutative property of addition.

The answer is the commutative property of addition.

#### Example 4

Identify which property is shown below.

First, notice that both sides of the equation have the same three addends in the same order, but the grouping has been changed. This is an example of the associative property of addition.

The answer is the associative property of addition.

#### Example 5

Find the value of

First, notice that both sides of the equation are the sum of two values. Also, both sides of the equation include the number 1.94 as one of the terms.

By the commutative property of addition, the second term must also be the same on both sides of the equation.

The answer is

### Review

Identify the property illustrated in each equation.

1.

2.

3.

4.

5.

6.

7.

8.

Find the value of

9.

10.

11.

12.

Solve each problem.

13. Lamont measures the amount of water he drinks. His results for four consecutive days were as follows: 0.6 liters, 0.72 liters, 0.84 liters, 0.96 liters. If the pattern continues, how much water will Lamont drink on the fifth day?

14. Barbara is starting a jewelry making enterprise. At the supply store, she spent $19.19 on beads and $6.81 on wire and clasps. If she left the store with $24.50, how much did she start with?

15. A rectangular playground has a length of 18.36 yards and a width of 12.24 yards. What is the perimeter of the playground?

### Answers for Review Problems

To see the Review answers, open this PDF file and look for section 2.6.

### Image Attributions

**[1]****^**Credit: Tony Webster; Source: https://www.flickr.com/photos/diversey/17489073452/; License: CC BY-NC 3.0

## Description

## Learning Objectives

In this concept, you will learn to identify and use the commutative and associative properties of addition with decimals.

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Dec 02, 2015## Last Modified:

Dec 02, 2015## Vocabulary

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