- MA.1.AR.2.3: Determine the unknown whole number in an addition or subtraction equation, relating three whole numbers, with the unknown in any position.Clarifications:Clarification 1: Instruction begins the development of algebraic thinking skills where the symbolic representation of the unknown uses any symbol other than a letter.
Clarification 2: Problems include the unknown on either side of the equal sign.
Clarification 3: Addition and subtraction are limited to sums within 20 and related subtraction facts. Refer to Situations Involving Operations with Numbers (Appendix A).