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Intro to Regrouping (When Adding & Subtracting)
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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?ANSWERAnswers will vary. The total amount should be 88.
10 ones blocks are equal to 1 tens block.
Yes, I can exchange 50 of them for 5 tens blocks. Then I have 2 ones blocks left over.
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.
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?ANSWERYes! 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.
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.
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 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.
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
Find the difference between two amounts.
- Add DEFINE
Put together two amounts.
- Place value DEFINE
The value of each digit based on its position in a number.
- Ones place DEFINE
Has a value of one.
- Tens place DEFINE
Has a value of ten ones.
- Regrouping DEFINE
Representing tens using ones, or representing ones using tens.
- Sum DEFINE
The result of adding.
- Difference DEFINE
The result of subtracting.
- Subtract DEFINE
- Reading Material
- Practice Word Problems
- Practice Number Problems
- Lesson Plan
- Teacher Guide