Primary Type: Lesson Plan
Status: Published
This is a resource from CPALMS (www.cpalms.org) where all educators go for bright ideas!
Resource ID#: 72907
The Mystery Of The Missing Number
This lesson uses a fun math mystery theme to help your students determine an unknown whole number to balance an equation.
Subject(s): Mathematics
Grade Level(s): 2
Intended Audience: Educators
Suggested Technology: Document Camera,
Computer for Presenter, Interactive Whiteboard
Instructional Time: 1 Hour(s) 30 Minute(s)
Resource supports reading in content area: Yes
Freely Available: Yes
Keywords: equal, whole number, equation, addition, subtraction, strategies
Resource Collection: FCR-STEMLearn Mathematics General
ATTACHMENTS
Prior Knowledge Formative Assessment.pdf
Summative Assessment.pdf
number cards.pdf
Equalizer Game.pdf
LESSON CONTENT
Lesson Plan Template: General Lesson Plan
Learning Objectives: What should students know and be able to do as a result of this lesson?
Students will determine the unknown whole number in an equation relating four whole numbers.
Students will explain the strategies or processes used to determine the unknown number in an equation.
Prior Knowledge: What prior knowledge should students have for this lesson?
Students should understand the meaning of the equal sign. MAFS.1.OA.47
Students should be able to determine the unknown whole number in an addition or subtraction equation relating to three whole numbers. MAFS.1.OA.4.8
Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. MAFS.1.OA.3.6
Guiding Questions: What are the guiding questions for this lesson?
1. What do you have to find out to solve the equation?
2. What do the numbers in the equation stand for or represent?
3. Where could you start?
4. Could you use objects or pictures to help you solve the equation?
5. What is the relationship between the quantities of this equation?
6. Does your solution balance the equation?
7. Can you explain the strategy that you used to solve the equation?
8. Can you think of another strategy to use?
Teaching Phase: How will the teacher present the concept or skill to students?
The teacher will begin the lesson by asking the students to raise their hands if they like mystery books. The teacher will ask the students to list
some of their favorite mystery books or stories. Some examples are: (A-Z Mysteries, Nancy Drew, Jigsaw Jones, Scooby-Doo Mysteries, Nate the Great, Cam
page 1 of 4 Jansen) The teacher will ask the students why they like mystery stories? The teacher will then tell the students that math also has mysteries
that need to be solved. The teacher will tell the students that the mystery they will be solving today is a missing number. When the students
see a "?" where a number should be, there is a mystery to solve. They will become detectives who are going to be using clues (strategies) to
help them find the answer.
The teacher will show a short video clip titled Math Mystery.
The teacher will use a document camera and write the equation 13 + 4 = 8 + ? on a sheet of paper placed under the camera. The teacher will ask the
students what the = sign means to them. After reviewing that the equal sign means that both sides have the same amount or same value, the teacher will
then ask the students where they would start to solve the equation (mystery). The teacher asks the students to explain their thinking or
strategies on how to solve the problem.
After the students have explained their strategies, the teacher will use multi-colored unifix cubes to represent each number of the equation. Red for 13, blue for 4,
green for 8, and yellow for ?. The teacher will model adding the red and blue cubes showing a total of 17. The teacher will ask if one side is 17, then what
must the other side total? The teacher will repeat correct student response. The teacher will have students give a strategy to help find how many more
yellow blocks will be needed to add to the 8 green blocks to also equal 17. The teacher will model using correct student strategies. (counting on, counting back,
make a ten, doubles)The teacher will have a student come up to the Document Camera and demonstrate their strategy. The teacher will ask the student to
explain how he/she got the answer. If a student has the wrong answer, have him/her talk through their strategies to help them find their error and make the
correction.
Celebrate with the students after solving each equation and finding the mystery number.
The teacher will then write another equation 11 - 5 = ? - 4. The teacher will ask what is different about this equation from the previous equation. The
students will explain that this problem is subtraction and that the ? mark is in a different place than the previous problem. The teacher will ask the students to
explain how to start the equation. The teacher will ask students to come up to the Elmo and show the representation of blocks to numbers in the
equation. The student can choose the color of the unifix cubes to represent each number and the missing number. The teacher will guide the students while they
are solving the equation by asking if 11 - 5 equals 6 then the number on the other side of the equation must be equal. Students need to be explaining their
strategies while solving or after solving the equation.
The teacher will write the following equation 18 - ? = 6 + 5. The teacher will ask the students what is different about this equation from the other
equations.
The teacher will ask the students to explain how to solve this mystery. What clues will they use?
Have students explain as they model the equation and solution with the unfix cubes.
The teacher will write the following equation 8 + 8 = 20 - ?
Follow the same steps as above.
Guided Practice: What activities or exercises will the students complete with teacher guidance?
The students will work in groups of 2.
The teacher will provide multi-colored unifix cubes for each group.
Students may use white boards, math journals, or paper to write their equations and strategies.
The teacher will write the equation 6 + 7 = ? + 9 on the white board.
The teacher will remind the students that they are solving the mystery of the missing number.
The teacher will also review that both sides of the equal sign must have the same value.
The students will work together to solve the equation. Students should write the steps they used on their white boards, journals, or paper.
The teacher will encourage students to explain their thought processes aloud to their partners as they solve the equation.
The teacher may ask what clues or strategies are you using to solve the equation.
The teacher will navigate the room checking for understanding or any difficulties that students may be having. The teacher will guide students to find any errors in
their equations and make corrections by questioning and having students explain their thinking aloud.
The teacher will provide the following equations on the white board for more guided practice.
Students will follow the above procedures as they solve the problems with their partner.
?+5=9-3
7 + ? = 10 + 4
15 - 7 = 6 + ?
? - 9 = 12 - 3
Independent Practice: What activities or exercises will students complete to reinforce the concepts and skills developed in the
lesson?
The students will now work independently rather than in pairs.
Each student will be given their own multi-colored unifix cubes to work with.
Allow any students to move away from the unifix cubes if they are ready.
The teacher will write the following equations on the white board.
1. 14 + ? = 8 + 8
2. 12 - 7 = 9 - ?
3. 6 + 7 = 16 - ?
The students will copy the equations into their math journal and solve the equations. The students will explain their steps and strategies.
The teacher will remind the students that they are solving the mystery while using clues/strategies to solve the equation.
The teacher will circulate the room, helping any students having difficulty and checking for understanding.
The teacher will give the Summative Assessment after the independent practice.
Closure: How will the teacher assist students in organizing the knowledge gained in the lesson?
The teacher will close the lesson by asking the students the following questions:
What does the equal sign mean to you? The students should be able to answer that it means balance. Each side of the equal sign should have the same value.
What strategies or clues did you use to find the mystery number? The students should be able to name count on, count back, mental math, doubles, doubles plus or
minus 1, addition and subtraction fact strategies.
What is something new that you learned today? Students may have balanced an equation for the first time with or without the unifix cubes. Students may mention
using a new strategy for the first time.
Can these strategies help you to solve other math problems? Encourage students to name other math problems they may encounter where these strategies will
come into use. For example: story problems, adding 3 or more digits, 2 or 3 digit subtraction.
page 2 of 4 Summative Assessment
The teacher will provide each student with two equations from the Summative Assessment Sheet. Students will determine the unknown whole number. Students will
solve equations in their Math Journal or on a half sheet of paper. Each student will be required to:
1. Write the meaning of the equal sign.
2. Write the equations and solve the equations.
3. Write the steps or strategies used to solve the equations.
Formative Assessment
Before beginning the lesson (the day before or the same day) to determine students prior knowledge the teacher will have students take out math journals, or pass
out a half sheet of white paper, or white boards. Write the following problems on the Interactive Whiteboard or white board.
1. 6+4 = 10
2. 3+2 = 5-1
3. 9-1 = 10-2
4. 7-5 = 2+3
5. 8 = 4+?
Have students copy the problems. Have students write what the equal sign tells them. Have students write the steps or strategies they used to solve the equations.
Students will write true or false next to the equation and make the equation true if it is false. The teacher will navigate the room checking each student's math journal
or paper using the checklist provided.
The teacher will use the Formative assessment checklist to determine any students who need remediation or extra help during the lesson. The checklist is also useful
for grouping students for remediation.
Feedback to Students
Throughout the guided and independent practice the teacher will need to circulate and ask some or all of the following questions to ensure student understanding:
1. What does the equal sign mean?
2. What do you have to find out to solve the equation?
3. What do the numbers in the equation stand for or represent?
4. Where could you start?
5. What is the relationship between the quantities of this equation?
6. Does your solution balance the equation? Does it make sense?
7. What can you do to fix your solution?
8. Can you explain the strategy that you used to solve the equation?
9. How do you know that?
While asking the questions and eliciting responses from the students, the teacher will need to check for accuracy, precision, and understanding. The teacher will
address any errors at this time by having the student explain their steps and strategies. This will provide the teacher with insight to help the student and also can help
the student identify his/her own error and make corrections.
ACCOMMODATIONS & RECOMMENDATIONS
Accommodations:
Provide hundreds charts for any students having difficulty with addition and subtraction facts.
Let students continue using the unfix cubes if they are not ready to move to the abstract.
Provide small group instruction/remediation for any students who did not master the skill.
Extensions:
Play the game called Equalizer.
Using number cards, the students will create equations that equal a specific number. Encourage students to work together and discuss the strategies that they are
using to make the equation.
Put students into groups of two. Students can sit next to one another or across from each other. The students are working together but will need to have different
equations.
Each pair of students will need 2 sets of number cards 0 through 10 and 2 sets of + and - cards .Each pair of students will need one set of 0 through 20 number
cards.
The students will place their set of number cards 0-10 face up in sequential order on the table in front of them. They will place their two + and two - cards next to
their numbers.
The set of 0 through 20 number cards will be placed face down in the middle of the two students.
One student will turn the top card face up from the deck and place it next to the deck.
Example: The student may turn over the card with a number 9.
Each student will use their own 0-10 number cards along with their + or - card to make an equation that equals 9.
Each student should have a different equation. Examples: 5 +4, 10 - 1, 6 + 4, 2 + 2 + 5
Each student will record their equation on a sheet of paper.
The next student will turn over a number from the 0-20 pile and the game continues.
The first group to reach 10 correct equations wins.
See attachments for photo examples.
Suggested Technology: Document Camera, Computer for Presenter, Interactive Whiteboard
Special Materials Needed:
page 3 of 4 Document Camera
Math Journals ( 1 per student)
Unifix Cubes
white board (1 per student)
dry erase marker (1 per student)
Further Recommendations:
This lesson can be continued using equations relating more than four whole numbers. Students will determine the whole number that makes the equation true. 10 +
12 + 8 = ? + 15
Additional Information/Instructions
By Author/Submitter
This lesson supports the following Math Practice Standard 2: Reason abstractly and quantitatively.
Video Clip titled Mystery Math created by Jill Mitchell through the following website http://goanimate4schools.com
Game "Equalizer" created by Dr. David Purpura and Jill Mitchell
SOURCE AND ACCESS INFORMATION
Contributed by: Jill Mitchell
Name of Author/Source: Jill Mitchell
District/Organization of Contributor(s): Charlotte
Is this Resource freely Available? Yes
Access Privileges: Public
License: CPALMS License - no distribution - non commercial
Related Standards
Name
MAFS.2.OA.1.a:
Description
Determine the unknown whole number in an equation relating four or more whole numbers. For example, determine
the unknown number that makes the equation true in the equations 37 + 10 + 10 = ______ + 18, ? – 6 = 13 – 4,
and 15 – 9 = 6 + .
page 4 of 4