Illustrative Mathematics: Finding Common Denominators to Subtract

Part (a) of this task asks students to use two different denominators to subtract fractions. The purpose of this is to help students realize that any common denominator will work, not just the least common denominator. Part (b) does not ask students to do it in more than one way; the purpose is to give them an opportunity to choose a denominator and possibly compare with another student who chose a different denominator. The two likely choices are the least common denominator and the product of the two denominators. Aligns with 5.NF.A.1.