Fraction Operations

Lesson 14

Math

Unit 5

4th Grade

Lesson 14 of 21

Objective


Add and subtract mixed numbers using a variety of mental strategies.

Common Core Standards


Core Standards

  • 4.NF.B.3.C — Add and subtract mixed numbers with like denominators, e.g., by replacing each mixed number with an equivalent fraction, and/or by using properties of operations and the relationship between addition and subtraction.

Criteria for Success


  1. Add and subtract mixed numbers using mental strategies, such as:
    1. Going up over a whole (as demonstrated by Student A in Anchor Task 1),
    2. Adjusting one addend (as demonstrated by Student B in Anchor Task 1), 
    3. Going down over a whole (as demonstrated by Student A in Anchor Task 2), or
    4. Converting a subtraction problem to an unknown addend one (as demonstrated by Student B in Anchor Task 2), among others. 
  2. (Optional) Simplify solutions by rewriting them using the largest possible unit.
  3. Estimate solutions and assess the reasonableness of answers based on estimates (MP.1).

Tips for Teachers


Similar to previous lessons in the unit, since it is possible to overemphasize the importance of simplifying fractions, the corresponding criteria for success and questions in the Anchor Tasks in Lessons 12–15 are optional. If you want the focus for today to solely be on adding and subtracting fractions using a variety of mental strategies, you may decide to cut this aspect of the lesson.

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Anchor Tasks

25-30 minutes


Problem 1

Two different students solved the problem $$1\frac9{10}+5\frac4{10}$$ below. Study their work and determine whether the strategy they used works.

Student A Student B

Guiding Questions

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Student Response

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Problem 2

Two different students solved the problem $$4\frac38-3\frac68$$ below. Study their work and determine whether the strategy they used works.

Student C Student D

Guiding Questions

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Student Response

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Problem 3

Solve.

$$1+\frac{5}{12}$$

$$\frac{11}{12} + \frac5{12}$$

$$8+4\frac36$$

$$7\frac56+4\frac36$$

$$1\frac1{10}-\frac1{10}$$

$$1\frac1{10}-\frac2{10}$$

$$1\frac1{10}-\frac4{10}$$

$$6\frac15-5$$

$$6\frac15-4\frac45$$

$$6\frac15-4\frac25$$

Guiding Questions

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Student Response

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References

Target Task

5-10 minutes


Solve. Show or explain your work. 

a.   $$1\frac{11}{12}+\frac5{12}$$

b.   $$6\frac15-4\frac45$$

Student Response

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Additional Practice


The Extra Practice Problems can be used as additional practice for homework, during an intervention block, etc. Daily Word Problems and Fluency Activities are aligned to the content of the unit but not necessarily to the lesson objective, therefore feel free to use them anytime during your school day.

Word Problems and Fluency Activities

Word Problems and Fluency Activities

Help students strengthen their application and fluency skills with daily word problem practice and content-aligned fluency activities.

Next

Solve word problems involving addition and subtraction of fractions.

Lesson 15
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Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Building, Adding, and Subtracting Fractions Less Than or Equal to 1

Topic B: Building, Adding, and Subtracting Fractions Less Than 2

Topic C: Building, Adding, and Subtracting Fractions Greater Than or Equal to 2

Topic D: Multiplication of Fractions

Topic E: Line Plots

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