Guided Lessons

# Mystery Addends: Representing Word Problems

Make a maths 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.
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Need extra help for EL students? Try theCircles in a CupPre-lesson.

Students will be able to use mental maths 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.

The adjustment to the whole group lesson is a modification to differentiate for children who are English learners.
(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.
• 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.
(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.
(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.
(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.
(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.
(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.