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Add & Subtract Within 100
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 Show answers to discussion questions
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 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 VideoHow can you break apart 26 using place value?ANSWER

26 = 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 VideoHow 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.

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

Reading Material
Download as PDF Download PDF View as Separate PageWHAT IS ADDING & SUBTRACTING WITHIN 100?You can break apart a number using place value to help you add. 24 is 2 tens and 4 ones. 24 = 20 + 4. When you break apart two numbers, you can add the tens then add the ones.
To better understand Adding & Subtracting within 100…
WHAT IS ADDING & SUBTRACTING WITHIN 100?. You can break apart a number using place value to help you add. 24 is 2 tens and 4 ones. 24 = 20 + 4. When you break apart two numbers, you can add the tens then add the ones. To better understand Adding & Subtracting within 100…LET’S BREAK IT DOWN!
PlaceValue Blocks
Place value is the value of a digit based on its position in a number. The 4 in 49 represents 4 tens. The 9 represents 9 ones. 49 = 40 + 9. You can use placevalue blocks to show 4 tens and 9 ones. Erika adds 1 more ones block to the pile. Now there are 10 ones. 10 ones is the same as 1 ten. Now there are 5 tens. 5 tens = 50. Try this one yourself: How can you represent 68 with placevalue blocks?
PlaceValue Blocks Place value is the value of a digit based on its position in a number. The 4 in 49 represents 4 tens. The 9 represents 9 ones. 49 = 40 + 9. You can use placevalue blocks to show 4 tens and 9 ones. Erika adds 1 more ones block to the pile. Now there are 10 ones. 10 ones is the same as 1 ten. Now there are 5 tens. 5 tens = 50. Try this one yourself: How can you represent 68 with placevalue blocks?Candy Apples
Erika has dipped 24 candy apples. Dane has dipped 35. How many candy apples have they dipped in all? Find 24 + 35. 24 is 2 tens and 4 ones. 35 is 3 tens and 5 ones. Add the ones and add the tens. 20 + 30 = 50. 4 + 5 = 9. The total is 50 + 9 = 59. Try this one yourself: Erika has dipped 33 candy apples. Dane has dipped 41 candy apples. How many have they dipped in all?
Candy Apples Erika has dipped 24 candy apples. Dane has dipped 35. How many candy apples have they dipped in all? Find 24 + 35. 24 is 2 tens and 4 ones. 35 is 3 tens and 5 ones. Add the ones and add the tens. 20 + 30 = 50. 4 + 5 = 9. The total is 50 + 9 = 59. Try this one yourself: Erika has dipped 33 candy apples. Dane has dipped 41 candy apples. How many have they dipped in all?Flowers
There are 58 blue flowers and 37 red flowers. How many flowers are there in all? Find 58 + 37. 58 is 5 tens and 8 ones. 37 is 3 tens and 7 ones. 50 + 30 = 80. 8 + 7 = 15. Altogether there are 8 tens and 15 ones. Regroup 10 ones as 1 ten. That makes 9 tens and 5 ones, or 95 in all. Try this one yourself: There are 48 yellow flowers and 36 purple flowers. How many flowers are there in all?
Flowers There are 58 blue flowers and 37 red flowers. How many flowers are there in all? Find 58 + 37. 58 is 5 tens and 8 ones. 37 is 3 tens and 7 ones. 50 + 30 = 80. 8 + 7 = 15. Altogether there are 8 tens and 15 ones. Regroup 10 ones as 1 ten. That makes 9 tens and 5 ones, or 95 in all. Try this one yourself: There are 48 yellow flowers and 36 purple flowers. How many flowers are there in all?Plastic Bricks
Erika has 65 blocks. She gives Dane 41 blocks. How many blocks does Erika have left? Find 65 – 41. 65 is 6 tens and 5 ones. 41 is 4 tens and 1 one. Subtract by place value. 60 – 40 = 20. 5 – 1 = 4. The answer is 2 tens and 4 ones, or 24. Erika has 24 bricks left. Try this one yourself: Erika has 87 blocks. She gives Dane 35 blocks. How many blocks does Erika have left?
Plastic Bricks Erika has 65 blocks. She gives Dane 41 blocks. How many blocks does Erika have left? Find 65 – 41. 65 is 6 tens and 5 ones. 41 is 4 tens and 1 one. Subtract by place value. 60 – 40 = 20. 5 – 1 = 4. The answer is 2 tens and 4 ones, or 24. Erika has 24 bricks left. Try this one yourself: Erika has 87 blocks. She gives Dane 35 blocks. How many blocks does Erika have left?Ant Farm
Dane has 71 ants in his ant farm. He gives Erika 38 ants. How many ants does Dane have left? Find 71 – 38. 71 is the same as 70 + 1. 38 is the same as 30 + 8. Try to subtract the ones. You can't take away 8 ones from 1 one. Regroup 1 ten in 71 as 10 ones. So 70 = 60 + 11. Subtract the ones. 11 – 8 = 3. Subtract the tens. 60 – 30 = 30. The difference is 30 + 3 = 33. Dane has 33 ants left. Try this one yourself: Dane has 82 worms. He gives Erika 49 worms. How many worms does Dane have left?
Ant Farm Dane has 71 ants in his ant farm. He gives Erika 38 ants. How many ants does Dane have left? Find 71 – 38. 71 is the same as 70 + 1. 38 is the same as 30 + 8. Try to subtract the ones. You can't take away 8 ones from 1 one. Regroup 1 ten in 71 as 10 ones. So 70 = 60 + 11. Subtract the ones. 11 – 8 = 3. Subtract the tens. 60 – 30 = 30. The difference is 30 + 3 = 33. Dane has 33 ants left. Try this one yourself: Dane has 82 worms. He gives Erika 49 worms. How many worms does Dane have left? 
Practice Word Problems

Practice Number Problems

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