4.

Relate Addition and Subtraction - 1st Grade Math

Understand that addition and subtraction are reverse operations, and visualize subtraction as an unknown addend problem. For example, 9 - 7 = ? can be viewed as 7 + ? = 9. Therefore, knowledge of addition facts can be used to solve subtraction problems. Students also construct and complete related addition and subtraction facts involving 3 numbers (fact families).

Common Core Alignment

1.OA.4Understand subtraction as an unknown-addend problem.