Given a two-digit number, mentally find 10 more or 10 less than the number, without having to
count; explain the reasoning used.

Compare two two-digit numbers based on meanings of the tens and ones digits, recording the results
of comparisons with the symbols >, =, and <.

Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions. (e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem)