Make a math mystery! In this lesson, help your students understand the relationship between addition and subtraction and how a missing addend word problem is represented with a number sentence.
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/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.
- 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
- GAME: Fish Bowl Addition
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.