Main content

## 2nd grade

### Course: 2nd grade > Unit 3

Lesson 2: Strategies for adding within 100- Breaking apart 2-digit addition problems
- Break apart 2-digit addition problems
- Adding 53+17 by making a group of 10
- Adding by making a group of 10
- Add 2-digit numbers by making tens
- Strategies for adding 2-digit numbers
- Select strategies for adding within 100

© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice

# Breaking apart 2-digit addition problems

Sal thinks about different ways to break up addition problems.

## Want to join the conversation?

- Which is the best subject to learn math with? I would like other problems with math too please.(2 votes)
- Maths is the foundation of almost all the sciences, so its hard to say at this level which would be a good subject to learn alongside math. Physics is the obvious answer. You'll find that most of physics is applied math. You could try watching the physics course, and when you come to a video or exercise that has too much math, stop watching and wait until you catch up with the math learning. Then you'll always have a reason to keep going and a problem you're trying to solve. Keep math the core of your forward progress and all the rest will open up to you, eventually. That's my hope, anyway.(25 votes)

- how do you break apart three digit numbers?(10 votes)
- To break apart 3 digit numbers, you separate the hundreds digit, the tens digit, and the ones digit. For example, if you were trying to break apart 729, you will separate the hundreds digit, which is 7, the tens digit, which is 2, and the ones digit, which is 9. So, 729 = 700 + 20 + 9.(12 votes)

- I still don't get it.(4 votes)
- I'll explain the steps

Let's do 83 + 11.

83 is 80 + 3

11 is 10 + 1

now it's 80 + 3 + 10 + 1

we can first add 80 + 10 which is 90

then add 3 + 1 which is 4

now we just add 90 + 4 which is 94

there, the answer to 83 + 11 is 94.(10 votes)

- how do you break apart four digit number(2 votes)
- By
**break apart**, do you mean switch to**standard form**? If so, lets imagine the number is 4,878

First, the**last digit**is the**ones place**. So, the 8 in the last digit is only equal to 8.

Second,**the second to last digit**is**the tens**. So, that is equal to 70.

Next, the**third to last digit**is the**hundreds**. So, the 8 there is equal to 800.

And finally, the**first number**is in the thousands. So the(6 votes)

- how do you add 39 + 61(3 votes)
- Well, try breaking it up.

30+60, and 9+1

30+60 is 90, because 3+6 is 9. And 9+1 is 10!! Meaning, 90+10 is 100, so your answer is 100.(3 votes)

- How can we do (Breaking apart 2-digit subtraction problems)

I did not understand this thing. 'Breaking apart 2-digit addition problems' is very clear to me. :)(3 votes)- When introducing 2 digit subtraction without regrouping, I always start with the base ten models. In addition to using base ten blocks, I also teach them to draw the blocks out on paper. This is because students won’t always have access to manipulatives, but they will have a pencil and paper. I always give my students a place value mat placed inside a plastic sleeve. This allows students to also write or draw using a dry erase marker and they can be used over and over again. Here is how this strategy works using the example 59-15=44

Build/draw out the minuend (59) with base ten blocks.

Take away the amount of the subtrahend (15). Remove 5 ones blocks and 1 tens block.

Count the remaining blocks left and solve for the difference.(3 votes)

- how do you break apart a 2-digit number(2 votes)
- we can break it into 1 and 10, like this

to break a number like 84 you would take 8 and add a zero to the end like 80 and add the 4.

so a broken up 84 would be 80 + 4.(1 vote)

- what do you broke up (2:56)(3 votes)
- He is saying that in the options, the numbers are represented as tens and ones, instead of a normal number. For example, in this case, the 41 is represented as 4 tens and 1 one; but a different way to broke up the numbers is to represent them as a normal number, so that would be 40 + 1.(3 votes)

- How do you break apart 6 digit number?(2 votes)
- Like you'd break apart any other number!

For example,

283,729

200,000 + 80,000 + 3,000 + 700 + 20 + 9(4 votes)

- Maths is the foundation of almost all the sciences, so its hard to say at this level which would be a good subject to learn alongside math. Physics is the obvious answer. You'll find that most of physics is applied math. You could try watching the physics course, and when you come to a video or exercise that has too much math, stop watching and wait until you catch up with the math learning. Then you'll always have a reason to keep going and a problem you're trying to solve. Keep math the core of your forward progress and all the rest will open up to you, eventually. That's my hope, anyway.(3 votes)

## Video transcript

- Let's think about ways to break up addition problems. And this is useful, because if we break them up in the right way, it might be easier for us to actually compute the addition. So let's look at this first question. Lindsay isn't sure how to add 39 plus 61. Help Lindsay by choosing an addition problem that is the same as 39 plus 61. So let's look at these choices. This first choose I have 30 plus 60 plus 90 plus ten. And I encourage you to pause the video and try to work this out actually before I do it. So this first choice, where do they get this 30 from? Well, 30, that's three tens, and I do have three tens right over here. The three in 39, that's in the tens place so it represents three tens or 30. And then we have 60, where did that come from? Well, in the number 61, the six is in the tens place, so it represents six tens or 60. And then we have plus 90. Now where is 90 coming from? I don't see the obvious 90 over here. It might be tempting to say, well I have a nine over here, but this is in the ones place, it's not in the tens place. This is nine, not 90. And over here I have one. I definitely don't have a 90. Or I definitely don't even have a ten. So this would make sense, instead of, if this didn't say 90, if this said nine, and instead of a ten, if this said one, 'cause we have a one in the ones place, then it would make sense, but it didn't say that. It didn't say 30 plus 60 plus nine plus one, It's saying 30 plus 60 plus 90 plus ten. So we're not gonna pick this choice. The next choice, we have 30 plus 60 plus nine plus one, which makes complete sense, because we have the 30 plus the nine, is going to be equal to 39. And then the 60 plus the one is going to be equal to 61. So these two things are equivalent. And the reason why it's useful to break up things this way, is 'cause you can compute in your head, 30 plus 60, that's three tens plus six tens is gonna be nine tens. So these two pieces right over here are going to be, that's going to be 90. And then nine plus one, that's gonna be ten. And then 90 plus ten, well that's going to be equal to 100. Now they didn't ask us to compute that, they're just saying, hey which of these are the same as what we have up above, and this one is definitely going to be the case. And we can only pick one here, so we're done, but we can verify that this one isn't gonna be right. We have the nine plus one, then they have three and six. Now this three here, that doesn't represent just three, that's three tens, that's 30. This should be 30. And this is six tens, not just six, so that should be 60, but that's not what they originally wrote. So we can rule that one out as well. Let's do another one. Which addition problem is the same as 41 plus 57? And here they broke up everything into, looks like tens and ones. So even before I look at the choices, let me see if I can do that. So 41, in the tens place I have four. So that's going to be four tens, and in the ones place I have one. Plus one one. That's 41. And then 57, 57 in the tens place, I have five, so plus five tens, and in the ones place I have seven. Plus seven ones. So let's see which of these choices is the same as what I just wrote here. So this first one, we have four tens and one one. Four tens and one one. Four tens and one one, that's 41, what I just... so this four tens plus one one would be 41. And then I also have, five tens and seven ones. Five tens and seven ones. So this first choice is exactly what I wrote down, it's just in a different order. If I write, four tens plus five tens plus one one plus seven ones. it's gonna be this first choice. And we know that we're done, but let's just look at the other choices to see why these don't make sense. So I see where the four tens come from, but then it has one ten. It looks like it's trying to take this one in a ones place and somehow turn it into a one ten, so that's definitely gonna be wrong. And then it says five ones, somehow this is five tens here, not five ones. So that doesn't make sense. And then this one says four ones, well this four, this is in the tens place, this is four tens. And then we have five ones, that five is in the tens place. It should be five tens. That should be tens, and that should be tens. So we feel good about the first choice.