Properties in Decimal
Operations
Jen Kershaw, M.ed
Kimberly Hopkins
Jen Kershaw
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Printed: January 28, 2016
AUTHORS
Jen Kershaw, M.ed
Kimberly Hopkins
Jen Kershaw
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C HAPTER
Chapter 1. Properties in Decimal Operations
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Properties in Decimal
Operations
In this concept, you will learn how to identify properties in decimal operations.
Let’s Think About It
Casey enjoys running. He plans to run 9.5 miles on Monday, 13.2 miles on Wednesday and 11.5 miles on Friday.
The next week, he plans to run 11.5 miles on Monday, 13.2 miles on Wednesday and 9.5 miles on Friday. Since
he runs different distances on different days, he’s confused that he ends up running the exact same number of miles
each week. Which property is represented by Casey’s situation?
In this concept, you will learn how to apply properties to decimals.
Guidance
A property is a rule that remains true when applied to certain situations in mathematics.
The commutative property means that you can switch the order of any of the numbers in an addition or multiplication problem and you will still reach the same answer.
4 + 5 + 9 = 18 is the same as 5 + 4 + 9 = 18
The order of the numbers being added does not change the sum of these numbers. This is an example of the
commutative property.
If you switch the order of the decimals in an addition problem, the sum does not change.
4.5 + 3.2 = 7.7 is the same as 3.2 + 4.5 = 7.7
The associative property means that you can change the groupings of numbers being added or multiplied and it
does not change the result. This applies to problems with and without decimals.
(1.3 + 2.8) + 2.7 = 6.8 is the same as 1.3 + (2.8 + 2.7) = 6.8
Notice that parentheses are used to help with the groupings.
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Sometimes, you will have a problem with a variable and a decimal in it. You can apply the commutative property
and associative property here too.
Let’s look at an example.
x + 4.5 is the same as 4.5 + x
(x + 3.4) + 5.6 is the same as x + (3.4 + 5.6)
The most important thing is that the order of the numbers and the groupings can change but the sum will remain the
same.
Guided Practice
Name the property illustrated below.
3.2 + (x + y) + 5.6 = (3.2 + x) + y + 5.6
First, check that all of the numbers and variables are the same on both sides of the equal sign.
yes
Next, determine if the order of the numbers and variables change or the groupings of the numbers and variables
change.
the groupings change
Then, determine the property.
associative property
The answer is that the associative property of addition changes.
Examples
Look at the following examples and name the property illustrated in each example.
Example 1
3.4 + 7.8 + 1.2 = 7.8 + 1.2 + 3.4
First, check that all of the numbers are the same on both sides of the equal sign.
yes
Next, determine if the order of the numbers changes or the groupings of the numbers changes.
the order changes
Then, determine the property.
commutative property
The answer is the commutative property of addition.
Example 2
(1.2 + 5.4) + 3.2 = 1.2 + (5.4 + 3.2)
First, check that all of the numbers are the same on both sides of the equal sign.
yes
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Chapter 1. Properties in Decimal Operations
Next, determine if the order of the numbers changes or the groupings of the numbers changes.
the groupings change
Then, determine the property.
associative property
The answer is the associative property of addition.
Example 3
x + 5.6 + 3.1 = 3.1 + x + 5.6
First, check that all of the numbers and variables are the same on both sides of the equal sign.
yes
Next, determine if the order of the numbers and variables change or the groupings of the numbers and variables
change.
the order changes
The answer is the commutative property of addition.
Follow Up
Remember Casey and his weekly runs? He runs 9.5 miles, 13.2 miles then 11.5 miles the first week and 11.5 miles,
13.2 miles and 9.5 miles the next week. Which property is represented by Casey’s two weeks of running?
9.5 + 13.2 + 11.5 = 11.5 + 13.2 + 9.5
First, check that all of the numbers are the same on both sides of the equal sign.
yes
Next, determine if the order of the numbers changes or the groupings of the numbers changes.
the order changes
Then, determine the property.
commutative property
The answer is the commutative property of addition. Casey’s two weeks of running represent the commutative
property.
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Video Review
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/167939
Explore More
Identify the property illustrated in each number sentence.
1. 4.5 + (x + y) + 2.6 = (4.5 + x) + y + 2.6
2. 3.2 + x + y + 5.6 = x + 3.2 + y + 5.6
3. 1.5 + (2.3 + y) + 5.6 = (1.5 + 2.3) + y + 5.6
4. 3.2 + 5.6 + 1.3 + 2.6 = 3.2 + 2.6 + 5.6 + 1.3
5. 4.5 + 15.6 = 15.6 + 4.5
6. (x + y) + 5.6 = x + (y + 5.6)
7. 17.5 + 18.9 + 2 = 2 + 17.5 + 18.9
8. (x + y) + z = x + (y + z)
9. 5.4 + 5.6 = 5.6 + 5.4
10. 1.2 + 3.2 + 5.6 = 1.2 + 5.6 + 3.2
11. 3.2 + (x + y) + 5.6 = 3.2 + x + (y + 5.6)
12. 3.4 + x + y + .6 = .6 + y + x + 3.4
13. 2.2 + 4.3 + 1.1 = 1.1 + 2.2 + 4.3
14. (1.2 + 3.4) + 7.6 = 1.2 + (3.4 + 7.6)
15. 8.9 + 9.3 + 3.1 = 9.3 + 8.9 + 3.1
Answers for Explore More Problems
To view the Explore More answers, open this PDF file and look for section 3.20.
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