# Mystery Addends: Representing Word Problems

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.
Need extra help for EL students? Try the Circles in a Cup pre-lesson.
##### View aligned standards
Need extra help for EL students? Try the Circles in a Cup pre-lesson.

#### 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.

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

#### 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.

Beginning

• Ask students to identify the larger number (18) and the smaller numbers (7 and 11). Model counting on from 11 to 18 as you think aloud, "11 + 7 = 18. If I know this fact, I also know that 7 + 11 = 18."
• Use manipulatives or a number line to show students that 18 - 7 = 11 and 18 - 11 = 7.
• Show students a few more examples of fact families before excusing them to make their own fact family triangles.

Intermediate

• Remind students that fact families include two addition and two subtraction facts. The number at the top is the sum, or total, of the two parts in the bottom corners.
• Write ________ + ________ = ________ and ________ - ________ = ________ on the board. Model solving for the third number in a fact family using both addition and subtraction.