The PDF linked below challenges a student to use knowledge of symbolic notation and functions to write an equation for two growing patterns. A student must be able to use the equation to extend the pattern and rearrange the equation to solve an inverse relationship. The student must be able to interpret the variables back to the context of the situation.
http://www.insidemathematics.org/common-core-math-tasks/high-school/HS-F-2003%20Conference%20Tables.pdf