1.OA.B.4

Understand subtraction as an unknown-addend problem. *For example, subtract 10 - 8 by finding the number that makes 10 when added to 8.*

Solve subtraction problems by thinking about what needs to be added to the subtrahend to reach the minuend. For example, 10 - 8 = __ can be solved by thinking about what needs to be added to 8 to reach 10. You could start your lesson by having students watch this video.