Adding and Subtracting Fractions

Adding and subtracting fractions with like denominators

http://www.khanacademy.org/math/arithmetic/fractions/Adding_and_subtracting_fractions/v/adding-fractions-with-like-denominators

Adding and subtracting fractions with unlike denominators

http://www.khanacademy.org/math/arithmetic/fractions/Adding_and_subtracting_fractions/v/adding-fractions-with-unlike-denominators