Addition and Subtraction of Fractions/Decimals

1. Find common units for fractions with unlike denominators by finding equivalent fractions using a number line, an area model, or using multiplication or division. 
2. Understand that there is more than one possibility for the common unit used, and use that to optionally find the least common denominator. 
3. Assess the reasonableness of an answer using number sense and estimation (MP.1).
4. Subtract two fractions with unlike denominators that require regrouping whose whole is between 1 and 2, simplifying and writing the sum as a mixed number, if applicable.
5. Solve one-step word problems involving the subtraction of two fractions with unlike denominators whose whole is less than 2 (MP.4).

For some problems in this lesson, students may use a computation-specific strategy. For example, students might think of a computation as an unknown-addend problem and use an addition strategy to solve (including the strategy of making a whole, e.g., to solve $$1\frac{3}{5}-\frac{7}{8}=1\frac{24}{40}-\frac{35}{40}$$, a student might add $$\frac{35}{40}+\frac{5}{40}=1$$ and $$1+\frac{24}{40}=1\frac{24}{40}$$, so the difference is $$\frac{5}{40}+\frac{24}{40}=\frac{29}{40}$$). Students might also use a strategy like going down over a whole (e.g., $$1\frac{24}{40}-\frac{24}{40}-\frac{11}{40}=1-\frac{11}{40}=\frac{29}{40}$$). Discussing various strategies and their advantages and disadvantages “provide opportunities for students to compare approaches and justify steps in their computations (MP.3)” (NF Progression, p. 13).

• Problem Set

• Problem Set Answer Key