How can you add tens numbers, like 40 + 50?

I know there are 4 tens + 5 tens. 4 + 5 = 9. There are 9 tens in all. 40 + 50 = 90.

How can you subtract tens numbers, like 60 – 40?

I know there are 6 tens to start. I can take away 4 tens from 6 tens. 6 – 4 = 2. There are 2 tens, or 20, left. 60 – 40 = 20.

How can place value help you to add numbers?

I can break apart numbers by their place values, and then add the separate place values together. For example, 82 = 80 + 2. 17 = 10 + 7. 80 + 10 = 90. 2 + 7 = 9. The final sum is 90 + 9 = 99.

When do you need to regroup when adding 2-digit numbers? How do you regroup?

I need to regroup if I add the ones and the number is 10 or greater. I regroup 10 ones as 1 ten.

Find 26 + 12. Do you need to regroup?

26 + 12 = 38. 20 + 10 = 30. 6 + 2 = 8. There are only 8 ones, so I don’t need to regroup.

When do you need to regroup when subtracting 2-digit numbers? How do you regroup?

I need to regroup if the number of ones I need to subtract is greater than the number of ones I'm subtracting from. I regroup 1 ten from the first number as 10 ones. For example, 34 – 29. I regroup 1 ten from 34 as 10 ones. So 34 = 20 + 14. Then I subtract the ones and the remaining tens.

Find 34 – 29. Do you need to regroup?

34 is 3 tens and 4 ones. 29 is 2 tens and 9 ones. 9 ones are more than 4 ones, so I need to regroup. 34 = 20 + 14. Subtract the ones. 14 – 9 = 5. Subtract the tens. 20 – 20 = 0. The answer is 5.

Add & Subtract Within 100

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What you will learn from this videoWhat you will learn

How to add and subtract numbers up to 100.
How regouping allows us to add and subtract numbers.
This knowledge can help us know the amount of flowers, desserts, and even how many ants that we have!

Discussion Questions
- Before Video
  How can you break apart 26 using place value?ANSWER
  - 26 = 20 + 6.
  Complete the equation. 58 = 50 + ___.ANSWER
  - 8.
  How can you add tens numbers, like 40 + 50?ANSWER
  - I know there are 4 tens + 5 tens. 4 + 5 = 9. There are 9 tens in all. 40 + 50 = 90.
  How can you subtract tens numbers, like 60 – 40? ANSWER
  - I know there are 6 tens to start. I can take away 4 tens from 6 tens. 6 – 4 = 2. There are 2 tens, or 20, left. 60 – 40 = 20.
  How can you show 18 ones using a ten and some more?ANSWER
  - 18 = 1 ten and 8 ones.
- After Video
  How can place value help you to add numbers?ANSWER
  - I can break apart numbers by their place values, and then add the separate place values together. For example, 82 = 80 + 2. 17 = 10 + 7. 80 + 10 = 90. 2 + 7 = 9. The final sum is 90 + 9 = 99.
  When do you need to regroup when adding 2-digit numbers? How do you regroup?ANSWER
  - I need to regroup if I add the ones and the number is 10 or greater. I regroup 10 ones as 1 ten.
  Find 26 + 12. Do you need to regroup?ANSWER
  - 26 + 12 = 38. 20 + 10 = 30. 6 + 2 = 8. There are only 8 ones, so I don’t need to regroup.
  When do you need to regroup when subtracting 2-digit numbers? How do you regroup?ANSWER
  - I need to regroup if the number of ones I need to subtract is greater than the number of ones I'm subtracting from. I regroup 1 ten from the first number as 10 ones. For example, 34 – 29. I regroup 1 ten from 34 as 10 ones. So 34 = 20 + 14. Then I subtract the ones and the remaining tens.
  Find 34 – 29. Do you need to regroup?ANSWER
  - 34 is 3 tens and 4 ones. 29 is 2 tens and 9 ones. 9 ones are more than 4 ones, so I need to regroup. 34 = 20 + 14. Subtract the ones. 14 – 9 = 5. Subtract the tens. 20 – 20 = 0. The answer is 5.
Vocabulary
- Place value DEFINE
- Add DEFINE
- Subtract DEFINE
- Sum DEFINE
- Difference DEFINE
- Expanded Form DEFINE
- Regroup DEFINE
Reading Material
Practice Word Problems
Practice Number Problems
Lesson Plan
Teacher Guide
Assessment
Online Quiz Game Quiz PDF Exit Ticket