What are 3 different ways to show 88 using base-ten blocks?

Answers will vary. The total amount should be 88.

How many ones blocks can you exchange for a tens block?

10 ones blocks are equal to 1 tens block.

You have 52 ones blocks. Can you exchange some of them for tens blocks?

Yes, I can exchange 50 of them for 5 tens blocks. Then I have 2 ones blocks left over.

How can you use ones and tens blocks to add 26 + 13?

2 tens blocks plus 1 tens block is 3 tens blocks. 6 ones blocks plus 3 ones blocks is 9 ones blocks. 3 tens blocks and 9 ones blocks is 39, so 26 + 13 = 39.

How can you use ones and tens blocks to subtract 38 – 24?

I can show 38 as 3 tens blocks and 8 ones blocks. 24 is 2 tens blocks and 4 ones blocks. I take away 2 tens from 3. 1 ten is left. I take away 4 ones from 8. 4 ones are left. I have 1 ten and 4 ones left, which is 14. 38 – 24 = 14.

Do you need to regroup when you add 25 + 15?

Yes! After adding, I have 3 tens blocks and 10 ones blocks. 10 ones blocks can be regrouped into 1 tens block, so I have 4 tens blocks, or 40.

Do you need to regroup to subtract 47 – 12?

No. 7 is greater than 2, so to subtract the ones, I can subtract 7 – 2. 4 is also greater than 1 so to subtract the tens, I can subtract 4 – 1. The answer is 35.

Do you need to regroup to subtract 47 – 19?

Yes. 7 is less than 9, so I cannot subtract 7 – 9. I have to borrow a ten and regroup it as 10 ones. I take one of the 4 tens blocks and regroup it into 10 ones blocks. Now I have 3 tens blocks and 17 ones block. I need to subtract 1 ten and 9 ones. To subtract the ones, I can subtract 17 – 9. To subtract the tens, I can subtract 3 – 1. The answer is 28.

Cathy wanted to add 28 + 43, so she regrouped everything into ones blocks and counted 71 blocks in all. She then regrouped them again into 7 tens blocks and 1 ones block. Did she get the right answer? Did she do it right?

Cathy got the right answer, but she did not have to regroup the two numbers into ones blocks first. She could have added together the tens and the ones, and then regrouped 10 of the ones into 1 ten.

Joey wanted to subtract 34 – 27, so he took 27 and regrouped one of the tens into 10 ones. What did he do wrong?

It does not help to regroup parts of 27. He should regroup 1 ten from 34 into 10 ones, because he needs more than 4 ones.

Intro to Regrouping (When Adding & Subtracting)

LESSON MATERIALS move

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What you will learn from this videoWhat you will learn

How regrouping can help us solve an addition problem.
How regrouping can help us solve a subtraction problem.
We’ll explore how this knowledge can help us count sea shells, feed pets and even eat donuts!

Discussion Questions
- Before Video
  What are 3 different ways to show 88 using base-ten blocks?ANSWER
  - Answers will vary. The total amount should be 88.
  How many ones blocks can you exchange for a tens block?ANSWER
  - 10 ones blocks are equal to 1 tens block.
  You have 52 ones blocks. Can you exchange some of them for tens blocks?ANSWER
  - Yes, I can exchange 50 of them for 5 tens blocks. Then I have 2 ones blocks left over.
  How can you use ones and tens blocks to add 26 + 13?ANSWER
  - 2 tens blocks plus 1 tens block is 3 tens blocks. 6 ones blocks plus 3 ones blocks is 9 ones blocks. 3 tens blocks and 9 ones blocks is 39, so 26 + 13 = 39.
  How can you use ones and tens blocks to subtract 38 – 24?ANSWER
  - I can show 38 as 3 tens blocks and 8 ones blocks. 24 is 2 tens blocks and 4 ones blocks. I take away 2 tens from 3. 1 ten is left. I take away 4 ones from 8. 4 ones are left. I have 1 ten and 4 ones left, which is 14. 38 – 24 = 14.
- After Video
  Do you need to regroup when you add 25 + 15?ANSWER
  - Yes! After adding, I have 3 tens blocks and 10 ones blocks. 10 ones blocks can be regrouped into 1 tens block, so I have 4 tens blocks, or 40.
  Do you need to regroup to subtract 47 – 12?ANSWER
  - No. 7 is greater than 2, so to subtract the ones, I can subtract 7 – 2. 4 is also greater than 1 so to subtract the tens, I can subtract 4 – 1. The answer is 35.
  Do you need to regroup to subtract 47 – 19?ANSWER
  - Yes. 7 is less than 9, so I cannot subtract 7 – 9. I have to borrow a ten and regroup it as 10 ones. I take one of the 4 tens blocks and regroup it into 10 ones blocks. Now I have 3 tens blocks and 17 ones block. I need to subtract 1 ten and 9 ones. To subtract the ones, I can subtract 17 – 9. To subtract the tens, I can subtract 3 – 1. The answer is 28.
  Cathy wanted to add 28 + 43, so she regrouped everything into ones blocks and counted 71 blocks in all. She then regrouped them again into 7 tens blocks and 1 ones block. Did she get the right answer? Did she do it right?ANSWER
  - Cathy got the right answer, but she did not have to regroup the two numbers into ones blocks first. She could have added together the tens and the ones, and then regrouped 10 of the ones into 1 ten.
  Joey wanted to subtract 34 – 27, so he took 27 and regrouped one of the tens into 10 ones. What did he do wrong?ANSWER
  - It does not help to regroup parts of 27. He should regroup 1 ten from 34 into 10 ones, because he needs more than 4 ones.
Vocabulary
- Subtract DEFINE
- Add DEFINE
- Place value DEFINE
- Ones place DEFINE
- Tens place DEFINE
- Regrouping DEFINE
- Sum DEFINE
- Difference DEFINE
Reading Material
Practice Word Problems
Practice Number Problems
Lesson Plan
Teacher Guide
Assessment
Online Quiz Game Quiz PDF Exit Ticket