In the previous grade, students subtract fractions with like denominators. In Subtract Fractions Worksheet, they subtract two fractions with unlike denominators. They do so by using their previous knowledge of equivalence of fractions to replace the fractions by those with like denominators. For example, 2/3 - 1/6 = 4/6 - 1/6 = 3/6. 

Common Core Alignment

5.NF.1Add and subtract fractions with unlike denominators (including mixed numbers) by replacing given fractions with equivalent fractions in such a way as to produce an equivalent sum or difference of fractions with like denominators.