Name
Number and Operations in Base Ten
5.NBT.7
Lesson 7
Addition
Properties
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Mackenzie practices violin four days a week. One week, she
practiced for 21, 39, 45, and 25 minutes. Use mental math
to find the total amount of time she practiced.
You can easily add 21 and 39. You can easily add 45 and 25.
So, group those numbers together.
21 + 39 + 45 + 25 = (21 + 39) + (45 + 25) Associative Property
= 60 + 70
Add. 21 + 39 = 60 and 45 + 25 = 70
= 130
Add. 60 + 70 = 130
So, Mackenzie practiced violin for 130 minutes.
Practice
Use properties of addition to find each sum mentally. Show
your steps and identify the properties that you used.
1. 9 + 6 + 31 =
46
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9 + 6 + 31 = 6 + 9 + 31
= 6 + (9 + 31)
= 6 + 40
= 46
2. 12.5 + 0 + 1 + 43.5 =
Commutative Property
Associative Property
Add.
Add.
57
12.5 + 0 + 1 + 43.5 = 1 + 12.5 + 43.5 + 0
= 1 + (12.5 + 43.5) + 0
= 1 + 56 + 0
= 57 + 0
= 57
Commutative Property
Associative Property
Add.
Identity Property
Add.
Lesson 7 My Homework345
Problem Solving
3. Sasha spent $1.05 on a soda, $5.25 on a sandwich, $0.75 on
a piece of fruit, and $4.95 on a magazine. Use mental math
to find the total amount she spent.
$12
4. Jessie went to the mall and bought a CD for $12.98,
a skirt for $17.50, a T-shirt for $8.50, and a bottle of
water for $1.02. Use mental math to find the total
amount she spent.
$40
5. Gary played soccer for 1 hour and tennis for 2 hours. Tanya
played tennis for 2 hours and soccer for 1 hour. Who played
sports longer? Explain.
They played for the same amount of time. According to the
Commutative Property, the order in which numbers are added does
not change the sum.
5
6.
Use Math Tools Without calculating, would
0.4 + (2 + 0.6) be less than, greater than, or equal to 3? Explain.
Test Practice
7. Paula was reading a novel. She read 13 pages on Sunday,
12 pages on Tuesday, 17 pages on Friday, and 8 pages on Saturday.
Use mental math to find the total number of pages she read.
A
40 pages
C
50 pages
B
42 pages
D
60 pages
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Sample answer: equal to; 0.4 + 0.6 = 1 and 1 + 2 = 3.