Fact Families

As werew going more in to depth with our addition and subtraction, we're learning how numbers are related.  The students have mastered the Commutative Property for addition.  For example 6+4=10 and 4+6=10.  We're also learning about fact Families.  This is using 3 numbers to create 2 addition and 2 subtraction problems.
For example, if our numbers are 3, 9, 12 these would be our fact family problems:
3+9=12, 9+3=12, 12-9=3 and 12-3=9.
We decided to have the students be the numbers and build the number sentences.