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Adding Common Fractions

Lesson Plan

Adding Common Fractions

Objectives

In this unit, students are introduced to the concept of adding fractions. Students will:

  • write addition equations and inequalities with fractions.
  • develop “operation sense” relating to adding common fractions.
  • develop estimation skills.
  • solve addition problems involving fractions.

Essential Questions

How are relationships represented mathematically?
How can mathematics support effective communication?
How is mathematics used to quantify, compare, represent, and model numbers?
What does it mean to estimate or analyze numerical quantities?
What makes a tool and/or strategy appropriate for a given task?
  • How is mathematics used to quantify, compare, represent, and model numbers?
  • How are relationships represented mathematically?
  • What does it mean to estimate or analyze numerical quantities?
  • What makes a tool and/or strategy appropriate for a given task?

Vocabulary

  • Decimal: A number written using base ten place values, includes a decimal point.
  • Decimal Fraction: A numerical fraction with 10 or 100 as its denominator, written to show the fractional place values after a decimal point.
  • Denominator: In a fraction, the number or quantity below the fraction bar. Tells the number of equal parts into which a whole is divided.
  • Fraction: Notation used to represent part of a whole or part of a group by telling the number of equal parts in the whole (denominator), and the number of those parts being described (numerator).
  • Inequality: A mathematical sentence that contains a symbol (<. >, ≤, ≥, or ≠) in which the terms on either side of the symbol are unequal.
  • Mixed Number: The sum of a whole number and a fraction.
  • Numerator: In a fraction, the number or quantity above the fraction bar. Tells the number of parts of a whole being described.
  • Unit Fraction: A fraction with a numerator of 1.

Duration

60–90 minutes

Prerequisite Skills

Prerequisite Skills haven't been entered into the lesson plan.

Materials

  • construction paper circles
  • scissors
  • glue

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Related Materials & Resources

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Formative Assessment

  • View
    • Observe during lesson activities and classroom discussion. Make sure that students are not overlapping fraction pieces and that the pieces fit exactly.

Suggested Instructional Supports

  • View
    Scaffolding, Active Engagement, Metacognition, Modeling, Explicit Instruction
    W: Students look at a sharing problem and determine what fraction of a cookie each child receives. 
    H: Students use fraction circles or strips to explore adding fractions as well as comparing fractions. 
    E: Students examine how fractions can be combined to rename a fraction. Students write addition equations and inequalities with fractions. 
    R: The class reviews what they learned about combining fractions and discusses the relationships they discovered when combining fractions. 
    E: Students move on to subtracting fractions by using models. 
    T: The lesson may be tailored to meet student needs. For a lesser challenge, students may use their fraction models to add fractions with the same denominator. For a greater challenge, students may extend the idea of adding fractions by using fractions greater than one. 
    O: Students use different fraction models to help them add and subtract fractions and to demonstrate understanding of the concepts. 

Instructional Procedures

  • View

    Present the following problem: “Sally has three cookies. She wants to share them equally between three friends and herself. How much will each child have?” Ask, “Will the amount be more than one cookie or less than one cookie? How do you know?”

    Provide three circles for each student to represent the cookies and allow them to experiment with the circles to simulate the situation. Write the following on the board and have students complete the exercise at their desks.

    Answer Key:

    Draw what each child receives.

    (Students are likely to divide each cookie into equal fourths and indicate that each child will get one-fourth of each cookie, or half of one cookie and one-fourth of the third cookie.)

    Amount of cookie:   

    Write the number sentence that describes how they shared the cookie.

    Possible answers:

     

    or

     

    Discuss with students that  by allowing them to use their circles as a model. Have students explore the question, “Why doesn’t ?” Have students represent their ideas in different ways, such as:

    • relating the fractions to  and 1
    • using fraction circles or fraction strips
    • changing the fractions to a common unit:
    • relating to other contexts, such as money ($0.50 + $0.25) or time ( hour +  hour)

    Record student answers on the board using a table like the one that follows.

    Why doesn’t  ?

     

     

     

     

     

     

     

     

     

     

     

    Emphasize that  could be represented by adding  or  using the fraction circles or fraction strips.

    Now that students are familiar with the benchmark fractions of 0, , , and 1, have them identify which of the following inequalities are true or false. (You may or may not allow students to use manipulatives.)

    • “True or False:  ?” (True)
    • “True or False:  ?” (False)
    • “True or False:  ?” (True)

    “We are now going to work in pairs to write number sentences and use fraction circles or strips to model them.” Write the following four numbers on the board: , and 1. Have pairs choose one of these numbers and use the fraction models (fraction circles or fraction strips) to represent adding two fractions to equal their chosen number. Ask students to write the number sentences they have modeled. Next, have them find two other fraction models (sections) that add up to the number they chose and write the matching addition sentence. For example, if students chose the number , they might combine  and  to equal , or . Another option would be to combine  and  to equal , or .

    When students can easily combine two fraction sections, have them combine three, and then four fraction sections. Encourage students to discuss fraction relationships as they explore the fraction sections. For example,  could be represented as . These should also include combinations of identical fraction sections. Students should explore equivalent representations for the fractions, such as .

    Encourage students to repeat the process to find combinations of fractions that are greater than 1. Use the following three mixed numbers: , , and .

    “Now we will move on to inequalities. Remember that an inequality compares two unequal values. You will be doing the same task you just completed but using an inequality symbol instead of an equal sign.” Have students use fraction models to find three fractions whose sum is less than 1 (a whole), and then write the matching addition sentence for the inequality. For example, . Afterward, have students find four fractions that have a sum greater than 1 and ask them to write the resulting statement of inequality.

    Bring the class back together and have students reflect on their work by focusing on the characteristics of numbers that fit a certain requirement. Allow students to make connections to other contexts such as money (decimals) to help them think about the fractions and estimates. Ask the following questions:

    • “If you add a fraction to itself and the sum is greater than 1, what must be true about the fraction?”  (The fraction is greater than .)
    • “If you add a fraction to itself and the sum is greater than , what must be true of the fraction?”  (The fraction is greater than .)
    • “If two fractions are both greater than 1, what must be true of their sum?”  (The sum must be greater than 2.)
    • “If two fractions are both greater than , what must be true of their sum?”  (The sum is greater than 1.)
    • “If a fraction is added to itself and the sum is less than , what must be true about the fraction?” (The fraction is less than .)

    Optional: Students could work in pairs on the questions, exploring different or higher-level possibilities. Give students a few minutes to work, and then have them share their results and solution methods. Be sure that they focus on the ideas involved and not the computation mechanics. This encourages students to think about fractional relationships and estimation.

    Extension:

    • Routine: Display one fraction addition problem and have students use their fraction models to represent the problem and write the appropriate equation.
    • Small Group: Divide the class into pairs and have students write problems like these on an index card:  and . Have students work together to model each addition sentence using a fraction circle. Repeat the activity using different denominators such as 5 or 8.
    • Expansion: For students who have mastered adding fractions, move them into subtracting fractions. Have them start with a section (fraction circles or fraction strips) representing . Guide them in representing the subtraction of  from  by using a  section from their fraction circles or strips to cover as much of the  section as possible. “You used your one-third piece to cover as much of the one-half piece as possible. Let’s find out how much remains to be covered. This is the same as writing . Which of your fractional pieces would cover the remaining section?” (A one-sixth piece.)

      Write on the board: . Have students work on the following tasks in pairs or small groups. Be sure to involve finding pairs of fractions that differ by more than or less than a specified amount.
    • Find two fractions that differ by more than .
    • Find two fractions that differ by more than .
    • Find two fractions that differ by more than .

    Problems such as these can help students develop number sense about common fractions by determining their differences.

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Final 05/16/2013
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