The purpose of the activity is to for students to internalize the idea of solving equations by using the inverse operation. Incidently, this is the same idea behind a lock, digital or physical. Anyone familiar with encoder rings will recognize their similarity to combination locks.
Students will learn the basics of a shift cypher and apply that knowledge to encrypting and decrypting messages. After the teacher has debriefed the activity, the class will apply their understanding of shift cyphers to solving one-step equations with the operation of addition.
Students grouped into pairs
scratch paper for each student
use variables to represent an unknown value
add and subtract positive and negative integers
solve equations through the process of inverting the operator
experience a relevant external application of solving equations: locking and unlocking
reinforce the idea of subtraction as adding an additive inverse