1.OA.A.1
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.
Addition and subtraction word problems within 20, including missing numbers in all positions. Examples:
Paul caught 6 fish. He caught 1 more than Greg. How many fish did Greg catch? This problem translates to 6 – 1 = __?
Sarah has 3 fewer stickers than Jody. Sarah has 4 stickers. How many does Jody have? This problem translates to 4 + 3 = __?
Here's an interesting variant where the sum is given.