Colorado Common Core Standards
CO.4.2. Patterns, Functions, and Algebraic Structures
4.2.1. Number patterns and relationships can be represented by symbols. Students can:
4.2.1.a. Generate and analyze patterns and identify apparent features of the pattern that were not explicit in the rule itself. (CCSS: 4.OA.5)
4.2.1.a.ii. Use a symbol to represent and find an unknown quantity in a problem situation.
4.2.1.a.iv. Find the unknown in simple equations.