Super Sleuths: Cracking Missing Number Mysteries!

Math Grades 1st Grade 5:43 Video
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Lesson Description

Let's become math detectives and solve problems with missing numbers using addition and subtraction! We'll use fun strategies to find the hidden numbers and become number ninjas.

Video Resource

Missing numbers in addition and subtraction | 2nd grade | Khan Academy

Khan Academy

Duration: 5:43
Watch on YouTube

Key Concepts

  • Addition and Subtraction Relationships
  • Finding Missing Numbers
  • Using Number Lines as a Strategy

Learning Objectives

  • Students will be able to identify the missing number in addition and subtraction equations.
  • Students will be able to use different strategies, like number lines, to solve for the missing number.
  • Students will be able to explain their reasoning when solving missing number problems.

Educator Instructions

  • Introduction (5 mins)
    Begin by asking students if they've ever lost something. Relate this to how sometimes numbers are 'missing' in math problems. Explain that today they'll become math detectives to find those missing numbers!
  • Watch and Discuss (10 mins)
    Watch the Khan Academy video 'Missing numbers in addition and subtraction | 2nd grade | Khan Academy'. Pause the video at different points to ask students what Sal is doing and why. Focus on the strategies he uses (adding to reach a round number, using subtraction).
  • Practice Together (10 mins)
    Write some example problems on the board (e.g., 10 = __ + 4, 15 - __ = 8, __ + 5 = 12). Guide students through solving these problems using the strategies from the video. Encourage students to share their thinking aloud.
  • Independent Practice (10 mins)
    Give students worksheets with similar problems to solve on their own. Circulate to provide support and answer questions.
  • Wrap Up (5 mins)
    Review the key concepts and strategies learned during the lesson. Ask students to share one thing they learned or found helpful.

Interactive Exercises

  • Number Line Challenge
    Provide students with number lines. Give them missing number problems, and have them use the number line to visually 'jump' forward or backward to find the answer.
  • Equation Building Blocks
    Use building blocks or counters to represent the numbers in the equation. Physically remove or add blocks to demonstrate how to find the missing number.

Discussion Questions

  • What does it mean for a number to be 'missing' in a math problem?
  • What are some different ways we can find the missing number?
  • How can knowing addition help us solve subtraction problems, and how can knowing subtraction help us solve addition problems?

Skills Developed

  • Problem Solving
  • Critical Thinking
  • Number Sense

Multiple Choice Questions

Question 1:

What number + 3 = 5?

Correct Answer: 2

Question 2:

7 - What number = 4?

Correct Answer: 3

Question 3:

What number + 2 = 8?

Correct Answer: 6

Question 4:

9 - What number = 6?

Correct Answer: 3

Question 5:

5 + What number = 10?

Correct Answer: 5

Question 6:

12 - What number = 7?

Correct Answer: 6

Question 7:

What number + 4 = 9?

Correct Answer: 5

Question 8:

11 - What number = 5?

Correct Answer: 7

Question 9:

6 + What number = 11?

Correct Answer: 5

Question 10:

13 - What number = 8?

Correct Answer: 6

Fill in the Blank Questions

Question 1:

4 + _______ = 7

Correct Answer: 3

Question 2:

9 - _______ = 2

Correct Answer: 7

Question 3:

_______ + 5 = 9

Correct Answer: 4

Question 4:

10 - _______ = 3

Correct Answer: 7

Question 5:

2 + _______ = 6

Correct Answer: 4

Question 6:

8 - _______ = 5

Correct Answer: 3

Question 7:

_______ + 1 = 5

Correct Answer: 4

Question 8:

6 - _______ = 1

Correct Answer: 5

Question 9:

5 + _______ = 8

Correct Answer: 3

Question 10:

7 - _______ = 0

Correct Answer: 7

Educational Standards

CCSS.Math.Content.1.OA.D.8:Determine the unknown whole number in an addition or subtraction equation relating three whole numbers. For example, determine the unknown number that makes the equation true in each of the equations 8 + ? = 11, 5 = _ - 3, 6 + 6 = _. CCSS.Math.Content.1.OA.B.4:Understand subtraction as an unknown-addend problem. For example, subtract 10 - 8 by finding the number that makes 10 when added to 8. CCSS.Math.Content.1.OA.C.6:Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 - 4 = 13 - 3 - 1 = 10 - 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 - 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).

Teaching Materials

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