Unlocking Subtraction Secrets: Regrouping Fun!

Math Grades 1st Grade 3:10 Video
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Lesson Description

Learn how to subtract one-digit numbers from two-digit numbers by regrouping tens and ones, just like Sal in the Khan Academy video!

Video Resource

Subtracting a 1-digit number with regrouping | 2nd grade | Khan Academy

Khan Academy

Duration: 3:10
Watch on YouTube

Key Concepts

  • Place Value (Tens and Ones)
  • Regrouping (Decomposing a Ten)
  • Subtraction

Learning Objectives

  • Students will be able to identify the tens and ones in a two-digit number.
  • Students will be able to explain the concept of regrouping a ten into ones.
  • Students will be able to subtract a one-digit number from a two-digit number using regrouping.

Educator Instructions

  • Introduction (5 mins)
    Start by reviewing place value. Ask students: 'What does the number 35 mean? How many tens are there? How many ones?' Use physical manipulatives like base-ten blocks to represent numbers. Briefly introduce the idea that sometimes we need to 'borrow' from the tens place when subtracting.
  • Video Viewing (7 mins)
    Play the Khan Academy video 'Subtracting a 1-digit number with regrouping | 2nd grade | Khan Academy'. Pause at key moments to ask clarifying questions. For example, when Sal regroups, ask 'Why is he moving the ten? What does it become?'
  • Guided Practice (10 mins)
    Work through example problems on the board, such as 42 - 5 and 26 - 9, using the same visual representation as the video (drawing tens and ones). Emphasize the steps of regrouping: crossing out a ten, adding ten ones to the ones place, and then subtracting.
  • Independent Practice (10 mins)
    Provide students with worksheets containing subtraction problems that require regrouping. Encourage them to draw tens and ones to help them solve the problems.
  • Wrap-up (3 mins)
    Review the key steps of regrouping and answer any remaining questions. Highlight the importance of understanding place value in subtraction.

Interactive Exercises

  • Regrouping with Blocks
    Provide students with base-ten blocks. Give them a subtraction problem (e.g., 23 - 7). Have them physically represent the number 23 with blocks. Then, guide them through the process of regrouping (trading one ten-block for ten one-blocks) to be able to subtract 7.
  • Whiteboard Subtraction
    Divide the class into pairs. Give each pair a whiteboard and marker. Call out subtraction problems (e.g., 31 - 4). Have them work together to solve the problem on the whiteboard, drawing tens and ones to show their regrouping.

Discussion Questions

  • What happens when you don't have enough ones to subtract?
  • Why is it important to understand tens and ones when we subtract?
  • Can you think of a time when you've had to 'borrow' something to solve a problem?

Skills Developed

  • Place Value Understanding
  • Subtraction with Regrouping
  • Problem-Solving

Multiple Choice Questions

Question 1:

What does 23 mean?

Correct Answer: 2 tens and 3 ones

Question 2:

When do we need to regroup?

Correct Answer: When we don't have enough ones

Question 3:

If we regroup 1 ten, how many ones do we get?

Correct Answer: 10

Question 4:

What is 35 - 8?

Correct Answer: 27

Question 5:

In the number 41, how many tens are there?

Correct Answer: 4

Question 6:

What is another word for 'regrouping'?

Correct Answer: Borrowing

Question 7:

If you have 2 tens and 15 ones, what number do you have?

Correct Answer: 35

Question 8:

Which place do we regroup from?

Correct Answer: Tens place

Question 9:

If you need to take away 6 ones, but you only have 2, what should you do?

Correct Answer: Regroup from the tens place

Question 10:

What does the number 1 in the tens place mean?

Correct Answer: Ten

Fill in the Blank Questions

Question 1:

The number 46 has 4 ____ and 6 ones.

Correct Answer: tens

Question 2:

When we regroup, we are '______' a ten.

Correct Answer: borrowing

Question 3:

If you regroup 1 ten, you get ___ ones.

Correct Answer: 10

Question 4:

In 32 - 5, we need to ______.

Correct Answer: regroup

Question 5:

The number 58 has 5 tens and ___ ones.

Correct Answer: 8

Question 6:

Taking away is called _________.

Correct Answer: subtraction

Question 7:

Regrouping helps us when we don't have enough ______.

Correct Answer: ones

Question 8:

After regrouping, the tens place is one _____ than before.

Correct Answer: less

Question 9:

30 + 5 is the same as the number _____.

Correct Answer: 35

Question 10:

We regroup from the _____ place.

Correct Answer: tens

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: 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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