Solving Subtraction Mysteries: Finding the Missing Number!

Mathematics Grades 3rd Grade 7:43 Video
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Lesson Description

Learn how to find the missing number in subtraction problems using fact families and inverse operations. Become a subtraction detective!

Video Resource

How to Subtract Unknown Numbers

Miacademy Learning Channel

Duration: 7:43
Watch on YouTube

Key Concepts

  • Fact Families
  • Inverse Operations (Subtraction)
  • Borrowing in Subtraction

Learning Objectives

  • Students will be able to identify the missing number in a subtraction problem.
  • Students will be able to use fact families to solve subtraction problems with unknowns.
  • Students will be able to solve subtraction problems with borrowing to find unknown numbers.

Educator Instructions

  • Introduction (5 mins)
    Begin by explaining that today, students will become subtraction detectives, solving mysteries to find missing numbers in subtraction problems. Briefly review what subtraction is and its relationship to addition.
  • Fact Families Review (5 mins)
    Remind students about fact families and how they relate addition and subtraction. Show a simple example like 2 + 3 = 5, 3 + 2 = 5, 5 - 2 = 3, and 5 - 3 = 2. Explain that we can use this idea to find missing numbers.
  • Video Explanation (7 mins)
    Play the "How to Subtract Unknown Numbers" video from Miacademy Learning Channel. Encourage students to pay attention to how Ashley uses fact families and moves numbers around to solve for the unknown.
  • Guided Practice (10 mins)
    Work through example problems similar to those in the video. Start with simpler problems like 5 - ? = 3 and gradually increase the difficulty, including problems that require borrowing, such as 46 - ? = 9. Model the process of rewriting the problem and solving for the unknown.
  • Independent Practice (10 mins)
    Provide students with a worksheet or online activity with subtraction problems with missing numbers. Encourage them to use the strategies they learned from the video and guided practice. Circulate and provide support as needed.
  • Wrap-up and Review (3 mins)
    Review the key concepts and strategies from the lesson. Ask students to share what they learned and any challenges they faced. Reinforce the idea that finding the missing number is like solving a puzzle.

Interactive Exercises

  • Number Bond Subtraction
    Use number bonds to visually represent subtraction problems and find the missing number. For example, if the total is 8 and one part is 3, students need to find the other part.
  • Subtraction Detective Game
    Create a simple game where students have to solve subtraction problems with missing numbers to earn points or rewards.

Discussion Questions

  • How can knowing addition facts help us solve subtraction problems?
  • What is a fact family, and how does it relate to subtraction?
  • When do we need to borrow in subtraction, and how does it work?

Skills Developed

  • Problem-solving
  • Critical Thinking
  • Number Sense
  • Fluency with subtraction

Multiple Choice Questions

Question 1:

What is the missing number in 7 - ? = 2?

Correct Answer: 5

Question 2:

Which number sentence is in the same fact family as 4 + 5 = 9?

Correct Answer: 9 - 4 = 5

Question 3:

What do we do when we can't subtract because the top number is smaller?

Correct Answer: Borrow

Question 4:

What is the missing number in 25 - ? = 10?

Correct Answer: 15

Question 5:

Which problem can help you solve ? - 3 = 6?

Correct Answer: 6 + 3 = ?

Question 6:

What does 'inverse operation' mean?

Correct Answer: The opposite of an operation

Question 7:

What is the missing number in 12 - ? = 5?

Correct Answer: 7

Question 8:

When we 'borrow', where does the extra ten come from?

Correct Answer: The tens place

Question 9:

What is the missing number in 100 - ? = 50?

Correct Answer: 50

Question 10:

If 11 - 5 = 6, what's the missing number in ? + 5 = 11?

Correct Answer: 6

Fill in the Blank Questions

Question 1:

We can use ______ ______ to help us find missing numbers in subtraction.

Correct Answer: fact families

Question 2:

The opposite of subtraction is ________.

Correct Answer: addition

Question 3:

When the top number is too small, we need to ________ from the next place value.

Correct Answer: borrow

Question 4:

If 8 - ? = 3, then 8 - 3 = ______.

Correct Answer: 5

Question 5:

In the problem 15 - 7 = 8, the number 7 is being ________ from 15.

Correct Answer: subtracted

Question 6:

The missing number in 20 - ____ = 10 is 10.

Correct Answer: 10

Question 7:

A fact family shows the relationship between addition and ________.

Correct Answer: subtraction

Question 8:

Finding the missing number is like solving a ________.

Correct Answer: puzzle

Question 9:

We use ________ value to help us borrow correctly.

Correct Answer: place

Question 10:

Subtraction means taking ________ from a number.

Correct Answer: away

Educational Standards

3.A.2.1:Use number sense with the properties of addition, subtraction, and multiplication, to find unknowns (represented by symbols) in one-step equations. Generate real-world situations to represent number sentences. 3.N.2.3:Use strategies and algorithms based on knowledge of place value and equality to fluently add and subtract up to five-digit numbers (answer not to exceed 100,000). 3.N.2.5:Use addition and subtraction to solve problems involving whole numbers. Use various strategies, including the relationship between addition and subtraction and the context of the problem to assess the reasonableness of results.

Teaching Materials

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