Subtraction Strategies: Cracking the Code of 3-Digit Numbers!

Mathematics Grades 4th Grade 4:43 Video
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Lesson Description

Learn different ways to subtract 3-digit numbers using strategies like breaking down numbers by place value and adjusting numbers to make subtraction easier. Get ready to become a subtraction superstar!

Video Resource

Methods for subracting 3 digit numbers

Khan Academy

Duration: 4:43
Watch on YouTube

Key Concepts

  • Place value (hundreds, tens, ones)
  • Breaking down numbers for easier subtraction
  • Adjusting numbers to create easier problems while maintaining the same difference

Learning Objectives

  • Students will be able to subtract 3-digit numbers using the strategy of breaking down the subtrahend (the number being subtracted) by place value.
  • Students will be able to adjust both the minuend (the number being subtracted from) and the subtrahend by adding or subtracting the same amount to simplify the subtraction problem.
  • Students will be able to explain why adjusting both numbers in a subtraction problem maintains the same difference.

Educator Instructions

  • Introduction (5 mins)
    Begin by asking students what they already know about subtraction. Discuss different strategies they may have used before. Introduce the idea that there are many ways to solve a subtraction problem and that they will learn some new methods today.
  • Video Viewing (10 mins)
    Play the Khan Academy video "Methods for Subtracting 3-Digit Numbers." Encourage students to take notes on the different strategies presented in the video.
  • Discussion: Breaking Down by Place Value (10 mins)
    Discuss the first strategy presented in the video: breaking down the number being subtracted by place value (hundreds, tens, ones). Work through a sample problem on the board, demonstrating this method. For example, 468 - 235 = 468 - 200 - 30 - 5.
  • Discussion: Adjusting Numbers (10 mins)
    Discuss the second strategy: adjusting both numbers to make the subtraction easier. Emphasize that if you add or subtract the same amount from both numbers, the difference stays the same. Work through a sample problem, such as 523 - 198. Discuss how adding 2 to both numbers makes the problem 525 - 200, which is easier to solve.
  • Practice Problems (15 mins)
    Provide students with a worksheet containing a variety of 3-digit subtraction problems. Encourage them to try using both strategies learned in the video. Circulate to provide assistance and answer questions.
  • Wrap-up (5 mins)
    Review the two strategies learned in the lesson. Ask students to share which strategy they prefer and why. Reiterate that there are multiple ways to solve math problems, and the best strategy depends on the individual and the problem.

Interactive Exercises

  • Subtraction Strategy Sort
    Create cards with different subtraction problems and have students sort them based on which strategy (breaking down by place value or adjusting numbers) would be most efficient to use.
  • Partner Subtraction Challenge
    Have students work in pairs. One student creates a 3-digit subtraction problem, and the other student solves it using one of the strategies learned. Then they switch roles.

Discussion Questions

  • Why does breaking down a number by place value help make subtraction easier?
  • Why is it important to add or subtract the *same* amount from both numbers when adjusting them for subtraction?
  • Can you think of a real-life situation where you might use these subtraction strategies?

Skills Developed

  • Subtraction of 3-digit numbers
  • Problem-solving
  • Strategic thinking
  • Number sense
  • Place Value

Multiple Choice Questions

Question 1:

What is one way to make subtraction easier with big numbers?

Correct Answer: Break down the numbers by their place value (hundreds, tens, ones)

Question 2:

If you add 5 to both numbers in a subtraction problem, what happens to the answer?

Correct Answer: The answer stays the same

Question 3:

Which place value is the 6 in the number 642?

Correct Answer: Hundreds

Question 4:

What is 458 - 100?

Correct Answer: 358

Question 5:

To make 367 - 199 easier, what could you do?

Correct Answer: Add 1 to both numbers

Question 6:

What is another word for the 'answer' to a subtraction problem?

Correct Answer: Difference

Question 7:

When breaking down 247 to subtract, what number represents the tens place?

Correct Answer: 40

Question 8:

If you are subtracting 15 from a number, what could you also subtract instead to make it easier?

Correct Answer: 1 ten and 5 ones

Question 9:

Which of the following equations shows the correct way to break down 582 by place value?

Correct Answer: 500 + 80 + 2

Question 10:

If you added 3 to both numbers of a subtraction problem and got an answer of 10, what would the answer be before you added 3 to both numbers?

Correct Answer: 10

Fill in the Blank Questions

Question 1:

When you subtract, you are finding the ___________ between two numbers.

Correct Answer: difference

Question 2:

The place value to the left of the tens place is the ___________ place.

Correct Answer: hundreds

Question 3:

To make subtraction easier, you can ____________ the number you're subtracting into hundreds, tens, and ones.

Correct Answer: break

Question 4:

If you add the same number to both parts of a subtraction problem, the answer stays the __________.

Correct Answer: same

Question 5:

When subtracting 10 from a number, only the _______ place changes.

Correct Answer: tens

Question 6:

In the number 729, the digit '2' represents ____ tens.

Correct Answer: 2

Question 7:

Changing a subtraction problem to an easier one is called ______ the numbers.

Correct Answer: adjusting

Question 8:

The strategy of breaking numbers apart relies on understanding _______ value.

Correct Answer: place

Question 9:

300 - 100 is easier to solve than 345 - 145 because you're only working with ___________.

Correct Answer: hundreds

Question 10:

Before you subtract, be sure to ______ your answer to see if it makes sense.

Correct Answer: estimate

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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