Use addition and subtraction within 100 to solve one- and two-step word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using drawings and equations with a symbol for the unknown number to represent the problem.
The big idea of this lesson is that addition and subtraction facts are related, and every subtraction fact has a related addition fact. Students can think of this inverse relationship when recalling basic subtraction facts.
The big idea of this lesson is that we can think of addition in the real world as the joining of two parts to make a whole. The use of addition number sentences can show how we join the parts to make the whole.
The big idea of this lesson is the understanding that the number relationships between 0 more than, 1 more than, and 2 more than lay the foundation for the basic addition facts with 0, 1, and 2.