Breaking Apart Numbers to Subtract: A Fun Way to Solve Problems!

Mathematics Grades 4th Grade 3:30 Video
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Lesson Description

Learn how to subtract numbers by breaking them into smaller, easier-to-manage parts! This lesson will help you become a subtraction superstar.

Video Resource

Subtraction by breaking apart

Khan Academy

Duration: 3:30
Watch on YouTube

Key Concepts

  • Breaking apart numbers into place values (hundreds, tens, ones).
  • Subtracting in stages to simplify calculations.
  • Understanding that changing both numbers in a subtraction problem by the same amount keeps the difference the same.

Learning Objectives

  • Students will be able to break apart numbers into hundreds, tens, and ones to simplify subtraction.
  • Students will be able to subtract multi-digit numbers by breaking them apart and subtracting in stages.
  • Students will be able to adjust both numbers in a subtraction problem to make calculations easier while maintaining the same difference.

Educator Instructions

  • Introduction (5 mins)
    Begin by asking students if they sometimes find it hard to subtract big numbers. Introduce the idea that we can make it easier by breaking the numbers into smaller parts, like hundreds, tens, and ones, just like the Khan Academy video will show us.
  • Video Viewing (10 mins)
    Play the Khan Academy video "Subtraction by breaking apart". Encourage students to pay attention to how the instructor breaks down the numbers and solves the subtraction problems step-by-step. Pause at key points to check for understanding.
  • Guided Practice (15 mins)
    Work through example problems on the board together. Start with problems similar to those in the video. For example: 567 - 234. Guide students to break down 234 into 200 + 30 + 4. Then subtract each part from 567: 567 - 200 = 367; 367 - 30 = 337; 337 - 4 = 333. Emphasize the importance of keeping track of each step.
  • Independent Practice (15 mins)
    Provide students with a worksheet containing subtraction problems that can be solved by breaking apart numbers. Encourage them to show their work and explain their steps. Include some problems where they can adjust both numbers, like the second example in the video (e.g., 356 - 198 can become 358 - 200).
  • Wrap-up (5 mins)
    Review the key concepts of breaking apart numbers for subtraction. Ask students to share any challenges they faced and how they overcame them. Reiterate that this strategy can make subtraction easier and more manageable.

Interactive Exercises

  • Number Decomposition Game
    Divide the class into teams. Present a subtraction problem (e.g., 642 - 315). Each team must break down the second number (315) into hundreds, tens, and ones as quickly as possible. The first team to correctly decompose the number earns a point. Continue with different subtraction problems.
  • Adjusting Numbers Challenge
    Present problems where adjusting numbers can simplify the subtraction (e.g., 431 - 99, 786 - 297). Challenge students to find the easiest way to adjust both numbers to make the subtraction simpler. For example, 431 - 99 can become 432 - 100.

Discussion Questions

  • Why do you think breaking apart numbers makes subtraction easier?
  • Can you think of a time when you used a similar strategy in real life?
  • How does breaking apart numbers help you understand place value better?

Skills Developed

  • Subtraction
  • Place Value Understanding
  • Problem Solving
  • Mental Math

Multiple Choice Questions

Question 1:

What is the first step in breaking apart a number to subtract?

Correct Answer: Break the number into hundreds, tens, and ones.

Question 2:

Which of these is the correct way to break apart the number 456?

Correct Answer: 400 + 50 + 6

Question 3:

To solve 789 - 234 by breaking apart, what do you subtract first?

Correct Answer: Subtract 200 from 789.

Question 4:

If you add 2 to both numbers in a subtraction problem, what happens to the answer?

Correct Answer: The answer stays the same.

Question 5:

Why might you want to change 298 to 300 when subtracting?

Correct Answer: Because subtracting 300 is easier than subtracting 298.

Question 6:

What is 678 minus 400?

Correct Answer: 278

Question 7:

What is 345 minus 20?

Correct Answer: 145

Question 8:

What is 987 minus 7?

Correct Answer: 980

Question 9:

What is 523 minus 1?

Correct Answer: 522

Question 10:

What is the value of the 8 in 853?

Correct Answer: 800

Fill in the Blank Questions

Question 1:

Breaking apart numbers helps make __________ easier.

Correct Answer: subtraction

Question 2:

When you break apart 325, you get 300 + 20 + __________.

Correct Answer: 5

Question 3:

If you add 1 to both numbers in a subtraction problem, the difference stays the ___________.

Correct Answer: same

Question 4:

To make 456 - 99 easier, you can change it to 457 - ___________.

Correct Answer: 100

Question 5:

The value of the '5' in 567 is __________.

Correct Answer: 500

Question 6:

When breaking apart 672, you separate the hundreds place, which is _________.

Correct Answer: 600

Question 7:

If you want to make 783 - 90 easier to solve, you can subtract the _________ place.

Correct Answer: tens

Question 8:

The ones place in 459 has a value of __________.

Correct Answer: 9

Question 9:

When breaking apart 924, you have 900 + ________ + 4

Correct Answer: 20

Question 10:

The 7 in 712 has a value of _________.

Correct Answer: 700

Educational Standards

4.N.2.4:Apply and analyze models to solve multi-step problems requiring the use of addition, subtraction, and multiplication of multi-digit whole numbers. Use various strategies, including the relationship between operations, the use of appropriate technology, and the context of the problem to assess the reasonableness of results. 4.N.2.5:Use strategies and algorithms (e.g., mental strategies, standard algorithms, partial quotients, repeated subtraction, the commutative, associative, and distributive properties) based on knowledge of place value, equality, and properties of operations to divide a 3-digit dividend by a 1-digit whole number divisor, with and without remainders.

Teaching Materials

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