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### Lesson plan

# Mystery Addends: Representing Word Problems

#### 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.

#### 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

*(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.

#### 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.

#### 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.