Lesson 11

The purpose of this lesson is for students to practice subtracting fractions with unlike denominators.

This lesson complements the previous lesson except that students are looking to make the greatest or smallest differences rather than sums. Trying to make the greatest difference supports strategies like students used in the previous lesson, looking to choose a large numerator and small denominator for one fraction and a small numerator and large denominator for the other (MP7). Trying to make a small difference brings a new feature into play, namely that the difference can be 0 if the fractions are equivalent. Other than looking for equivalent fractions, students may also realize that if both fractions are small, then their difference will also be small.

• Each group of 2 needs a paper clip.

How effective were your questions in supporting students’ thinking today? What did students say or do that showed they were effective?