Standard
- CCSS.Math.Content.1.NBT
- Number and Operations in Base Ten
- CCSS.Math.Content.1.NBT.C
- Use place value understanding and properties of operations to add and subtract.
- CCSS.Math.Content.1.NBT.C.5
- Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.