Lesson Plan:

Mystery Addends: Representing Word Problems

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September 5, 2015
by Dwayne Slobodnick

Learning Objectives

Students will be able to use mental math to solve missing addend questions using both addition and subtraction strategies. Students will be able to represent a given missing addend word problem using a number sentence. Students will be able to identify the initial, change, and result of a word problem.

Lesson

Introduction (10 minutes)

  • Tell the students that today they will be reviewing fact families, or related numbers, and they will use that knowledge to help them represent missing addend word problems.
  • Remind your students that an addend is a number in a problem that is being added.
  • Show the example of a fact family triangle to the students, and have them explain the relationship between the 3 numbers.
  • Tell the students that they will make their own fact family triangles and play a game with them.
  • Pass out the triangles, and have the students each write out a fact family.
  • Then, have them walk around the room to find a partner to answer the question.
  • Direct each student to cover up one of the 3 numbers and show it to his partner.
  • Next, have your students find new partners and do it again.
  • After they have asked several peers, have them sit down.
  • Instruct your students to keep the triangles in their desks to play later.

Explicit Instruction/Teacher Modeling (10 minutes)

  • Write a word problem on the board similar to one on the worksheet.
  • Read it aloud to the class and explain your thinking to them, reasoning how the sentences tell you the starting and ending amounts.
  • Use the key terms initial, or beginning, and change, or difference, when discussing the missing addends to help the students visualize the story.

Guided Practice/Interactive Modeling (10 minutes)

  • Write a new word problem on the board similar to the one during the explicit instruction.
  • This time, have the class read out the question, and have students go through sentence by sentence to locate the addends for the initial and change.
  • Ask the students to help you write down the number sentence that represents the word problem using a ∆ (triangle) to represent the mystery addend.
  • Then, change the word problem a little to switch the mystery addend, and then have the students explain how they would answer that one.

Independent Working Time (20 minutes)

  • Explain to the students that they will independently do what they just practiced with you on the board.
  • Handout the Missing Addend Word Problem worksheets, and have the students cut out the number sentences and match them to the word problems.
  • When students finish this, instruct them to pair up and discuss why they chose the number sentence they did for each word problem.
  • As the students are doing this, walk around and conference with students and document their thinking.
  • When you notice that the students have done their pair-sharing, choose some students to share what they did and why.

Extend

Differentiation

  • Enrichment: For advanced students, ask them to make their own missing addend word problems, and have their peers write number sentences to represent them.
  • Support: Give students manipulatives, or instruct them to draw a picture of the word problem to help them visualize it.

Related Books and/or Media

Review

Assessment (5 minutes)

  • Make sure your students are correctly representing the missing addend word problems with number sentences.
  • Walk around as your students are completing the assignment, checking their initial and change amounts.

Review and Closing (5 minutes)

  • After the students share their answers as a class, write down a couple of number sentences on a piece of chart paper to show missing addends.

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