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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?ANSWER26 = 20 + 6.
8.
I know there are 4 tens + 5 tens. 4 + 5 = 9. There are 9 tens in all. 40 + 50 = 90.
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.
18 = 1 ten and 8 ones.
After Video
How can place value help you to add numbers?ANSWERI 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.
I need to regroup if I add the ones and the number is 10 or greater. I regroup 10 ones as 1 ten.
26 + 12 = 38. 20 + 10 = 30. 6 + 2 = 8. There are only 8 ones, so I don’t need to 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.
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
The value of a digit based on its location in a number.
- Add DEFINE
To bring two or more numbers (or things) together to make a new total.
- Subtract DEFINE
To take one number away from another.
- Sum DEFINE
The result of adding.
- Difference DEFINE
The result of subtracting.
- Expanded Form DEFINE
A form of a number that shows a number as the sum of the value of its digits. For example, 234 = 200 + 30 + 4.
- Regroup DEFINE
Exchanging 10 ones for 1 ten, or 1 ten for 10 ones.
- Place value DEFINE
- Practice Word Problems
- Practice Number Problems
- Lesson Plan
- Teacher Guide
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