Detective Math: Finding Missing Numbers!

Math Grades 1st Grade 5:21 Video
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Lesson Description

Become a math detective and learn how to find missing numbers in addition and subtraction problems using fact families!

Video Resource

Finding the unknown number - 1st Grade Math (1.OA.8)

Boddle Learning

Duration: 5:21
Watch on YouTube

Key Concepts

  • Fact Families (related addition and subtraction equations)
  • Inverse Relationship between Addition and Subtraction
  • Using Subtraction to find Missing Addends

Learning Objectives

  • Students will be able to identify the missing number in addition and subtraction equations.
  • Students will be able to use fact families to solve for unknown numbers.
  • Students will be able to explain the relationship between addition and subtraction.

Educator Instructions

  • Introduction (5 mins)
    Begin by reviewing addition and subtraction. Ask students: 'What happens when we add numbers together?' and 'What happens when we subtract?' Introduce the idea that sometimes we don't know all the numbers in a math problem, and it's our job to find them!
  • Video Viewing (5 mins)
    Play the Boddle Learning video: 'Finding the unknown number - 1st Grade Math (1.OA.8)'. Encourage students to pay attention to how the video uses fact families to find the missing numbers.
  • Guided Practice (10 mins)
    Work through examples similar to those in the video. Start with addition problems like 3 + ? = 10 and then move to subtraction problems like 14 - ? = 10 and ? - 5 = 8. Emphasize using subtraction to solve addition problems and addition to solve subtraction problems when the minuend is unknown.
  • Independent Practice (10 mins)
    Provide students with worksheets or math manipulatives to solve similar equations independently. Circulate the room to provide support and answer questions.
  • Wrap Up (5 mins)
    Review the main concepts of the lesson. Ask students to explain in their own words how they find the missing numbers. Preview the next lesson.

Interactive Exercises

  • Number Bond Activity
    Use number bonds to visually represent fact families. Give students a number bond with one number missing and have them fill it in using addition or subtraction.
  • Missing Number Game
    Write addition and subtraction equations on index cards with a blank space for the missing number. Have students take turns drawing a card and filling in the missing number.

Discussion Questions

  • What is a fact family?
  • How can subtraction help you solve an addition problem?
  • How can addition help you solve a subtraction problem when you are missing the first number?
  • Why is it important to know how addition and subtraction are related?

Skills Developed

  • Problem-solving
  • Critical thinking
  • Number sense
  • Understanding of mathematical relationships

Multiple Choice Questions

Question 1:

Which number is missing? 2 + ___ = 5

Correct Answer: 3

Question 2:

Which number is missing? 7 - ___ = 3

Correct Answer: 5

Question 3:

Which number is missing? ___ + 4 = 9

Correct Answer: 5

Question 4:

Which number is missing? 10 - ___ = 6

Correct Answer: 5

Question 5:

Which number is missing? ___ - 2 = 8

Correct Answer: 10

Question 6:

What is a fact family?

Correct Answer: Related addition and subtraction equations

Question 7:

If 4 + 3 = 7, then what is 7 - 3?

Correct Answer: 4

Question 8:

Which helps you solve for a missing number in addition?

Correct Answer: Subtraction

Question 9:

Which number is missing? 5 + ___ = 10

Correct Answer: 5

Question 10:

Which number is missing? ___ - 4 = 6

Correct Answer: 10

Fill in the Blank Questions

Question 1:

A fact _______ is a group of related addition and subtraction equations.

Correct Answer: family

Question 2:

We can use _______ to help us find the missing number in addition.

Correct Answer: subtraction

Question 3:

The missing number in 4 + ___ = 6 is ____.

Correct Answer: 2

Question 4:

The missing number in 9 - ___ = 5 is ____.

Correct Answer: 4

Question 5:

The missing number in ___ - 3 = 7 is ____.

Correct Answer: 10

Question 6:

If 2 + 5 = 7, then 7 - 5 = ____.

Correct Answer: 2

Question 7:

To find the missing number in ___ - 1 = 9, we can add 1 and 9. The missing number is ____.

Correct Answer: 10

Question 8:

The opposite of adding is ______.

Correct Answer: subtracting

Question 9:

When you subtract, the answer gets ______.

Correct Answer: smaller

Question 10:

When you add, the answer gets ______.

Correct Answer: bigger

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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