The Fraction Workbench - working w/ UNcommon Denominators

The easy challenge in this applet asks the user to decompose a fraction into the sum or difference of two fractions that have the same denominator. A harder challenge is to decompose a fraction into the sum or difference of two fractions with different denominators. Harder still is the challenge to decompose a fraction into two fractions neither of whose denominators is the same as that of the original fraction.