Lesson objective: Determine whether addition or subtraction is required to solve a word problem. Then apply the standard algorithms.

This lesson provides an opportunity for students to apply their knowledge and understanding of the standard algorithms for addition and subtraction to a mathematical situation. Students are asked to determine missing values in a population chart based on clues and apply the standard algorithms for addition and subtraction to solve.

Key Concept students will use:

- The meanings of addition and subtraction do not change depending on how we perform them.

Skills students will use:

- Students will apply place value concepts in whole number addition and subtraction.

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they determine whether to use addition or subtraction and apply the standard algorithms to solve.

**Key vocabulary: **

- addend
- algorithm
- expression
- regrouping