Page 48 - TB_5B

Learn about Associative and Commutative Properties of Addition.

Associative Property
The way addends are grouped does not change the sum.

(3+8)+5=3+(8+5)
( 2.4 + 1.2 ) + 4.8 = 2.4 + ( 1.2 + 4.8 )

Commutative Property
The order of the addends does not change the sum.

1+2+9=1+9+2
1.25 + 3.15 + 2.75 = 1.25 + 2.75 + 3.15

2 . Use Associative or Commutative Property of Addition to find the sum.

a. 52.1 + 8.3 + 12.9 = 73.3 b. 52.20 + ( 38.32 + 22.80 ) = 113.32

c. 0.371 + 8.3 + 0.129 = 8.8 d. ( 12.6 + 82.51 ) + 7.4 = 102.51

The following method can be used as well.

2.7 + 3.6 = ( 2 + 0.7 ) + ( 3 + 0.6 ) Separate the decimals and whole numbers.
= 2 + ( 0.7 + 3 ) + 0.6 Use the Associative Property of Addition.
= 2 + ( 3 + 0.7 ) + 0.6 Use the Commutative Property of Addition.
= ( 2 + 3 ) + ( 0.7 + 0.6 ) Use the Associative Property of Addition.
= 5 + 1.3
= 6.3

20. Adding and Subtracting Decimals 37