Common Core math · 1st grade
Treat subtraction as a missing-number adding problem.
1.OA.B.4 is part of the Common Core State Standards for Mathematics. Missing Number practices it. Standards vary by state, so check with your kid’s teacher for the exact match.
Missing Number: A balance scale has blocks on one side and a box on the other: how many go in the box to make both sides weigh the same? It's 4 + ? = 7 as a picture. The missing number moves from the end to the start of the sum, first within 10 and then within 20.