Relacionar Columnas Lesson 20 VocabularyVersión en línea Match the term and definition with the example. por Tracy Harrison 1 Variable: A letter that represents an unknown number. In some cases, a variable may represent more than one number. 2 Substitute: To replace one thing with another. 3 Equivalent Expressions: Two or more expressions in different forms that always name the same value. 4 Solution of an Equation: A value that can be substituted for a variable to make an equation true.