Length:
1 hour
Key Vocabulary
- Numerator
- Denominator
- Least common denominator
Curriculum Standards
- CCSS.Math.Content.5.NF.A.1
Add and subtract fractions with unlike denominators (including mixed numbers) by replacing given fractions with equivalent fractions in such a way as to produce an equivalent sum or difference of fractions with like denominators. For example, 2/3 + 5/4 = 8/12 + 15/12 = 23/12. (In general, a/b + c/d = (ad + bc)/bd.)
- CCSS.Math.Content.5.NF.A.2
Solve word problems involving addition and subtraction of fractions referring to the same whole, including cases of unlike denominators, e.g., by using visual fraction models or equations to represent the problem. Use benchmark fractions and number sense of fractions to estimate mentally and assess the reasonableness of answers. For example, recognize an incorrect result 2/5 + 1/2 = 3/7, by observing that 3/7 < 1/2.
Instructions
- Warm up students and prepare for learning by having them add and subtract fractions with like denominators. Review the concept and clarify for understanding.
- Tell students they will be learning about adding and subtracting unlike fractions and mixed numbers. Preview and pre-teach vocabulary, and have students take notes.
- Have students prepare for note taking by dividing a page in their notebooks into four sections and labeling each of the sections according to the four concepts discussed in the lesson:
- Adding Unlike Fractions
- Subtracting Unlike Fractions
- Adding Unlike Mixed Numbers
- Subtracting Unlike Mixed Numbers
- Show our Study.com video lesson How to Add and Subtract Unlike Fractions and Mixed Numbers.
- Pause at the following spots and review the steps for each calculation. Have students take notes and complete a practice problem in each of the sections.
- Adding Unlike Fractions: 1:48
- Subtracting Unlike Fractions: 3:05
- Adding Unlike Mixed Numbers: 4:39
- Subtracting Unlike Mixed Numbers: 6:07
- Watch the lesson summary. Ask:
- How is adding unlike fractions the same as adding unlike mixed numbers? How is it different?
- Why do we need to find the least common denominator to add or subtract unlike fractions and mixed numbers?
Activity
- Allow students to practice the four concepts discussed in the lesson by setting up four stations in your room, one for each operation. Prepare task cards of varying degrees of difficulty to differentiate. For example, some may include simple problems and others more complex word problems.
- Allow students to work in their notebooks, on whiteboards, or any other surface available. Provide manipulatives or visuals. Connect to our lesson by incorporating problems involving hamburgers, cooking or triathlons.
- Circulate the room to check for student understanding and assist when necessary.
Extensions
- Assign letters to numbers and fractions to create a secret code. Students can work on problems whose answers reveal a secret message.
- Have students role dice to find a numerator and denominator. Add or subtract and record in notebooks.
