Khan Academy Static

Substitution_evaluating_expressions

Learn how to substitute (or "plug in") values for variables and evaluate algebraic expressions.

Expression_value_intuition

Explore how the value of an algebraic expression changes as the value of its variable changes.

Intro_to_variables

Wait, why are we using letters in math? How can an 'x' represent a number? What number is it? This tutorial is great if you're just beginning to delve into the world of variables and expressions.

Writing_basic_algebraic_expressions_word_problems

Learn how to write algebraic expressions (expressions with variables) to model real-world situations.

Writing_algebraic_expressions_introduction

Learn the basics of writing expressions with variables.

Evaluating_expressions_word_problems

Learn how to plug in values to evaluate real-world expressions.