**Apply properties of operations as strategies to add and subtract.** Examples: If 8 + 3
= 11 is known, then 3 + 8 = 11 is also known. (Commutative property of addition.) To
add 2 + 6 + 4, the second two numbers can be added to make a ten, so 2 + 6 + 4 = 2 +
10 = 12. (Associative property of addition.)