&&66
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AF 1.1*2$
Use the commutative
and associative rules to simplify mental
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UNDERLYING SKILLS AND CONCEPTS:
calculations and to check results.
turnaround facts
Use Properties
a
K
ey Ide
Turn-around facts for addition show the
commutative property.
The associative property tells that you can change the
grouping of addends without changing the sum.
E x am p l E
1
5!7
Tim has 5 cards in his right hand.
He has 7 cards in his left hand.
How many cards does Tim have?
7!5
12
=
You can add two numbers in any order.
Mr. Commutative
5 ! 7 " 12 and 7 ! 5 " 12
5 ! 7 is the same as 7 + 5.
B – © CSL Associates, Inc. All rights reserved.
=
10 ! 7 ! 8
E x am p l E
2
!
Find the sum of 17 ! 8.
You can take apart numbers and regroup
the parts to make adding easier.
10 !
15
"2
You know that 17 is the same as 10 ! 7.
So you can solve (10 ! 7) ! 8.
The associative property tells that:
(10 ! 7) ! 8 " 10 ! (7 ! 8)
Find the basic fact. 7 ! 8 " 15
Then add the 10. So, 17 ! 8 " 25.
Chapter 5 – Lesson 4
(10 ! 7) ! 8
10 ! (7 ! 8)
12
=
=
Ms. Associative
page 57
Name
P RAC T I C E
Rewrite each problem with three addends. Then find the sum.
1
15 9 10 5 9 10 14 24
2
17 4 10 7 4 10 11 21
3
16 7 10 6 7 10 13 23
4
13 8 10 3 8 10 11 21
5
12 9 10 2 9 10 11 21
6
11 7 10 1 7 10 8
7
27 6 20 7 6 20 13 33
18
8
Maria used 17 red stickers and 9 yellow stickers.
Li-ping used 9 blue stickers and 17 green stickers.
Who used more stickers? Explain.
They used the same number. 17 9 26
and 9 17 26. They are turn-around facts.
Math
Reasoning
9
Algebra
MR 1.1
There are 37 marbles in all.
How many marbles are
in the last box?
10
page 58
?
Chapter 5 – Lesson 4
B – © CSL Associates, Inc. All rights reserved.
Solve.
Name
P RAC T I C E
Rewrite each problem with three addends. Then find the sum.
1
14 8 10 4 8 10 12 22
2
16 5 10 6 5 10 11 21
3
18 5 10 8 5 10 13 23
4
12 9 10 2 9 10 11 21
5
16 8 10 6 8 10 14 24
6
13 6 10 3 6 10 9
7
28 7 20 8 7 20 15 35
19
8
Ruth used 16 red pencils and 7 yellow pencils.
Mark used 7 blue pencils and 16 green pencils.
Who used more pencils? Explain.
They used the same number. 16 7 23
and 7 16 23. They are turn-around facts.
Math
Reasoning
9
Algebra
MR 1.1
There are 38 marbles in all.
How many marbles are
in the last box?
13
page 40
Home Resource and Homework
?
Chapter 5 Lesson 4
B – © CSL Associates, Inc. All rights reserved.
Solve.
MCX94TEG2Ch01_30.v9.4.1 2/19/01 19:45 Page 107
Name
P RAC T I C E
Rewrite each problem with three addends. Then find the sum.
1
15 9 10 5 9 10 14 24
2
17 4 10 7 4 10 11 21
3
16 7 10 6 7 10 13 23
4
13 8 10 3 8 10 11 21
5
12 9 10 2 9 10 11 21
6
11 7 10 1 7 10 8
7
27 6 20 7 6 20 13 33
18
B – © CSL Associates, Inc. All rights reserved.
Solve.
8
Maria used 17 red stickers and 9 yellow stickers.
Li-ping used 9 blue stickers and 17 green stickers.
Who used more stickers? Explain.
They used the same number. 17 9 26
and 9 17 26. They are turn-around facts.
Math
Reasoning
9
Algebra
MR 1.1
There are 37 marbles in all.
How many marbles are
in the last box?
10
Chapter 5 – Lesson 4
Student Book Page
?
page 58
Name
P RAC T I C E
Rewrite each problem with three addends. Then find the sum.
1
14 8 10 4 8 10 12 22
2
16 5 10 6 5 10 11 21
3
18 5 10 8 5 10 13 23
4
12 9 10 2 9 10 11 21
5
16 8 10 6 8 10 14 24
6
13 6 10 3 6 10 9
7
28 7 20 8 7 20 15 35
19
8
Ruth used 16 red pencils and 7 yellow pencils.
Mark used 7 blue pencils and 16 green pencils.
Who used more pencils? Explain.
They used the same number. 16 7 23
and 7 16 23. They are turn-around facts.
Math
Reasoning
9
Algebra
MR 1.1
There are 38 marbles in all.
How many marbles are
in the last box?
13
page 40
Home Resource and Homework
?
Chapter 5 Lesson 4
B – © CSL Associates, Inc. All rights reserved.
Solve.