Khan Academy
Khan Academy: Adding & Subtracting Rational Numbers
Practice adding and subtracting negative fractions, decimals, and percents. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
Other
Project Happy Child: Adding Fractions Story & Worksheets
Miss Walker explains to Bart the fine details of adding fractions. At the end of the discourse is a link, "Return to Fractions index," where you can go to print off some practice sheets.
Khan Academy
Khan Academy: Add and Subtract Mixed Numbers 2 (With Regrouping)
Practice adding and subtracting mixed numbers with common (like) denominators. Some items require regrouping. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.