This is Day 2 of a lesson focusing on the conceptual understanding aspect of 5.NF.2--using visual fraction models to add two fractions with unlike denominators. Building this conceptual understanding of using equivalence to add unlike denominators is an important precursor to using addition or subtraction to solve word problems with these types of fractions. This lesson highlights Core Action 1.
Adding Fractions with Unlike Denominators--Day 2 of 2 (Zafrin )Download
Here, the students are asked to create their own word problem similar to the trail mix example. The teacher plans for a variety of different student activities during this lesson in order to build student understanding around the grade-level content of adding fractions with unlike denominators.
Through the use of modeling and discussion, students come to the understanding that twelfths is an appropriate common denominator for equivalent fractions. The teacher asks students to articulate their understanding of why twelfths work, focusing on the conceptual understanding aspect of this content. As she works with this small group, she uses manipulatives and guided exploration to make the mathematics of the lesson clear.
In this part of the lesson, the teacher works with a small group where she models for students and asks questions to draw out an understanding of why certain numbers work as common denominators. One of the students explains why twelfths work as a common denominator in this situation, using more than one sentence (with minimal prompting) to explain his understanding.