Mentally find 10 more or 10 less than any two-digit number, without counting; explain the reasoning used.
Number Sense, Properties, and Operations
- Understand the structure and properties of our number system. At their most basic level numbers are abstract symbols that represent real-world quantities
The whole number system describes place value relationships within and beyond 100 and forms the foundation for efficient algorithms
Use place value and properties of operations to add and subtract.