Workshop: Add and Subtract Fractions

Estimate Sums and Differences. Begin the lesson by asking students to quickly estimate the sum or difference of two fractions. They should decide whether the exact answer is greater than or less than 1. Tell students to put their thumbs up to indicate “greater than 1” or their thumbs down to indicate “less than 1.” Display the following problems one at a time:

      1/2 + 2/3 (greater than 1; thumbs up)

      4/5 + 1/10 (less than 1; thumbs down)

      11/3 − 2/3 (less than 1; thumbs down)

      23/4 − 11/12 (greater than 1; thumbs up)

Direct students to the Workshop: Add and Subtract Fractions page in the Student Guide. Read the short vignette together and ask student to complete Questions 1–4 individually. Students should be given a short time to estimate whether the fraction sums and differences are greater than or less than 1. Upon completion, choose some of the problems and ask students to explain how they estimated the sum or difference.

Find Exact Sums and Differences. Continue reading the vignette on the page. In this section, Mr. Moreno challenges his class to find two fractions with a sum or difference that is between 1 and 2. Assign Question 5. Students check Mr. Moreno's class's work by finding exact sums and differences. As they work, circulate and select students to share an addition and a subtraction solution strategy with the class upon completion. Try to choose a student who can show a paper-and-pencil method, and select a student who can justify the answer with mental math, fraction circle pieces, or a number line.

Compare Addition and Subtraction Strategies. When students have finished, ask them to demonstrate the strategies they used to add and subtract the fractions found in Question 5. List examples of the variety of strategies they use on chart paper. Display the charts.

Display and direct students' attention to the Adding and Subtracting Fractions Menu in the Student Guide Reference section. See Figure 1. Ask them to compare the strategies found on the Menu to those they have listed on chart paper.

Encourage students to use the Adding and Subtracting Fractions Menu and the strategies displayed on the class charts as they solve the problems in the Workshop.