Oswego City School District
Regents Exam Prep Center: Adding and Subtracting Fractions
Use this site to learn how to add and subtract algebraic fractions, even if there aren't common denominators. Provides plenty of examples.
Help Algebra
Help algebra.com: Simplifying Rational Expressions
The process of factoring and canceling is used to simplify, multiply, and divide rational expressions. Adding and subtracting rational expressions is also demonstrated, including finding common denominators.