Lesson objective: Apply understandings of symbols within equations and the meaning of the equals sign to find unknown numbers and create true equations.

This lesson provides an opportunity for students to apply their knowledge and understanding of symbols representing unknown numbers within equations to a mathematical situation. Students are asked to determine unknown numbers within equations in order to replace symbols and create true equations.

Key Concept students will use:

- The unknown number in an equation will make the equation true and can be represented by a symbol.

Skills students will use:

- addition and subtraction skills within 20 with unknowns in all positions (Grade 1, Unit 9)
- various addition and subtraction strategies within 20 (Grade 1, Unit 9)
- understanding of the meaning of the equals sign (Grade 1, Unit 9)

Students engage in Mathematical Practice #4 (model with mathematics) as they determine the meaning and value of symbols and use addition strategies to justify their reasoning.

**Key vocabulary: **

- determine
- equation
- missing
- objects
- symbol
- true
- unknown

**Special materials needed:**

- Cookie Detective cards
- counters
- cubes