Use Properties for Mental Math

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evaluate simple algebraic expressions in one variable by
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UNDERLYING SKILLS AND CONCEPTS:
add, subtract, multiply, and divide with
whole numbers
Use Properties for Mental Math
You can use the properties of addition and multiplication to compute
using mental math.
Commutative Property of Addition:
Changing the order of the addends does not change the sum.
Commutative Property of Multiplication:
Changing the order of the factors does not change the product.
Distributive Property:
Multiplying a sum by a number is the same as multiplying each addend
by the number and then adding the products.
E x am p l E
1
Use mental math to find the sum of 18 ! 7 ! 2.
Use the commutative property of addition to write the addends in a different order.
E – © CSL Associates, Inc. All rights reserved.
18 ! 7 ! 2 " 18 ! 2 ! 7
" 20 ! 7
" 27
E x am p l E
2
Use mental math to find the product of 4 # 35.
Use the distributive property.
4 # 35 " (4 # 30) ! (4 # 5)
" 120 ! 20
" 140
page 104
Chapter 9 – Lesson 4
Name
P RAC T I C E
Use mental math to find each sum.
1. 35 7 3 45
2. 8 15 12 35
3. 54 9 1 64
4. 4 52 4 60
5. 15 72 5 92
6. 18 36 2 56
8. 28 5 2 280
9. 12 4 10 480
2 94 188
Use mental math to find each product.
E – © CSL Associates, Inc. All rights reserved.
7. 5 12 2 120
10. 3 42 126
11.
13. 21 7 147
14. 32 25 4 3,200
Math
Reasoning
12. 17 5 85
15. 50 93 2 9,300
Use Properties for Mental Math
MR 2.3
16. How does the commutative property help you find sums and products using mental
math?
I can change the order of the addends or factors so that I can do the
easy computations first.
Chapter 9 – Lesson 4
page 105
MCX94.HW.CL.G5.FM&Lesson.v211
8/2/04
18:02
Page 72
Name
…at home!
P RAC T I C E
Use mental math to find each sum.
1. 67 4 3 74
2. 6 36 14 56
3. 75 9 1 85
4. 3 82 8 93
5. 15 43 5 63
6. 16 34 2 52
8. 38 5 2 380
9. 15 4 5 300
2 73 146
Use mental math to find each product.
150
10. 4 42 168
11.
13. 22 8 176
14. 21 25 4 2,100
Math
Reasoning
12. 19 5 95
15. 50 2 68 6,800
Use Properties for Mental Math
MR 2.3
16. How does the commutative property help you find sums and products using mental
math?
I can change the order of the addends or factors so that I can do the
easy computations first.
page 72
Home Resource and Homework
Chapter 9 Lesson 4
E – © CSL Associates, Inc. All rights reserved.
7. 5 15 2 MCX94TEG5CH01_32.v7.4.2 2/24/01 19:44 Page 195
Name
P RAC T I C E
Use mental math to find each sum.
1. 35 7 3 45
2. 8 15 12 35
3. 54 9 1 64
4. 4 52 4 60
5. 15 72 5 92
6. 18 36 2 56
8. 28 5 2 280
9. 12 4 10 480
2 94 188
Use mental math to find each product.
E – © CSL Associates, Inc. All rights reserved.
7. 5 12 2 120
10. 3 42 126
11.
13. 21 7 147
14. 32 25 4 3,200
Math
Reasoning
12. 17 5 85
15. 50 93 2 9,300
Use Properties for Mental Math
MR 2.3
16. How does the commutative property help you find sums and products using mental
math?
I can change the order of the addends or factors so that I can do the
easy computations first.
Chapter 9 – Lesson 4
Student Book Page
page 105
Name
…at home!
P RAC T I C E
Use mental math to find each sum.
1. 67 4 3 74
2. 6 36 14 56
3. 75 9 1 85
4. 3 82 8 93
5. 15 43 5 63
6. 16 34 2 52
8. 38 5 2 380
9. 15 4 5 300
2 73 146
Use mental math to find each product.
150
10. 4 42 168
11.
13. 22 8 176
14. 21 25 4 2,100
Math
Reasoning
12. 19 5 95
15. 50 2 68 6,800
Use Properties for Mental Math
MR 2.3
16. How does the commutative property help you find sums and products using mental
math?
I can change the order of the addends or factors so that I can do the
easy computations first.
page 72
Home Resource and Homework
Chapter 9 Lesson 4
E – © CSL Associates, Inc. All rights reserved.
7. 5 15 2 
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