Tackling Two-Digit Subtraction: Regrouping to the Rescue!

Math Grades 1st Grade 5:26 Video
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Lesson Description

Learn how to subtract two-digit numbers when the ones digit on top is smaller than the ones digit on the bottom. We'll use regrouping (or borrowing) to make subtraction easier!

Video Resource

Subtracting with regrouping (borrowing) | Early Math | Khan Academy

Khan Academy

Duration: 5:26
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Key Concepts

  • Place Value (Tens and Ones)
  • Regrouping (Borrowing) a Ten
  • Subtraction with Two-Digit Numbers

Learning Objectives

  • Students will be able to identify the tens and ones place in a two-digit number.
  • Students will be able to explain the concept of regrouping (borrowing) a ten from the tens place to the ones place.
  • Students will be able to subtract two-digit numbers using regrouping when the ones digit on top is smaller.

Educator Instructions

  • Introduction (5 mins)
    Begin by reviewing place value (tens and ones) with students. Ask them to represent different two-digit numbers using base-ten blocks (if available) or drawings. For example, ask them to show 34 using blocks or drawings (3 tens and 4 ones).
  • Video Viewing (7 mins)
    Play the Khan Academy video 'Subtracting with regrouping (borrowing) | Early Math | Khan Academy'. Encourage students to follow along and pause the video to try solving the example problems independently.
  • Guided Practice (10 mins)
    Work through example problems on the board, demonstrating the process of regrouping. Use clear and simple language, emphasizing how taking a ten from the tens place adds ten to the ones place. Examples: 42 - 15, 61 - 28, 93 - 36
  • Independent Practice (10 mins)
    Provide students with worksheets containing subtraction problems that require regrouping. Circulate the classroom to offer assistance and support as needed.
  • Wrap-up and Review (3 mins)
    Review the main points of the lesson, emphasizing the importance of regrouping when the ones digit on top is smaller. Ask students to share any questions or difficulties they encountered.

Interactive Exercises

  • Base-Ten Block Regrouping
    Give students base-ten blocks (or use online manipulatives). Present a subtraction problem that requires regrouping (e.g., 32 - 17). Guide them to physically exchange a ten-block for ten one-blocks to model the regrouping process.
  • Place Value Chart Subtraction
    Provide students with place value charts. Have them write the numbers they are subtracting in the correct place. Then, guide them through the regrouping process using the chart to help visualize taking a ten from the tens column and adding it to the ones column.

Discussion Questions

  • What happens when the number on top in the ones column is smaller than the number on the bottom?
  • Why do we 'borrow' a ten from the tens place?
  • How does 'borrowing' a ten change the value of the number in the tens place?

Skills Developed

  • Subtraction
  • Place Value Understanding
  • Problem-Solving
  • Critical Thinking

Multiple Choice Questions

Question 1:

What does it mean to regroup in subtraction?

Correct Answer: To 'borrow' a ten from the tens place.

Question 2:

In the number 42, which number is in the ones place?

Correct Answer: 2

Question 3:

In the number 68, which number is in the tens place?

Correct Answer: 6

Question 4:

If you 'borrow' a ten from the tens place, how many ones do you add to the ones place?

Correct Answer: 10

Question 5:

What is 54 - 26?

Correct Answer: 28

Question 6:

What is 83 - 45?

Correct Answer: 48

Question 7:

Which problem needs you to regroup?

Correct Answer: 52-18

Question 8:

If you have 32 and take away a ten, how many tens are left?

Correct Answer: 2

Question 9:

What does it mean if you run out of ones to take away?

Correct Answer: You regroup!

Question 10:

What is 91-64?

Correct Answer: 27

Fill in the Blank Questions

Question 1:

When the top number in the ones place is smaller, we need to ________.

Correct Answer: regroup

Question 2:

When we regroup, we take a ____ from the tens place.

Correct Answer: ten

Question 3:

Taking a ten from the tens place gives us ____ ones.

Correct Answer: 10

Question 4:

In the number 75, the 7 is in the ____ place.

Correct Answer: tens

Question 5:

In the number 39, the 9 is in the ____ place.

Correct Answer: ones

Question 6:

Regrouping is also called ________.

Correct Answer: borrowing

Question 7:

The answer to a subtraction problem is called the ________.

Correct Answer: difference

Question 8:

If you regroup 42, you have 3 tens and ____ ones.

Correct Answer: 12

Question 9:

To regroup is to change the value but keep the number the ____.

Correct Answer: same

Question 10:

If you 'borrow' from the tens place to make 11 ones and you have 7 tens left, you know the number is ____.

Correct Answer: 71

Educational Standards

1.NBT.C.4:Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten. 1.NBT.B.2:Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases: CCSS.Math.Content.1.OA.A.1:Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.

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