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## Early math review

### Course: Early math review > Unit 5

Lesson 8: Subtraction within 100# Subtracting with regrouping (borrowing)

Sal subtracts 25 from 83 by thinking about tens and ones.

## Want to join the conversation?

- Does regrouping also apply to subtracting 3- or 4-digit numbers?(69 votes)
- Yes it does! :) It is the same as subtracting two digits, except there are more numbers.(81 votes)

- How do you solve 48-77=? i always get -31 as answer though it should be -29(10 votes)
- What you can do is reorder them, then subtract them like normal, then 'flip' the answer.
`77-48 = 29`

then put a minus on the`29`

to make it`-29`

and there's your answer!

By the way, I'm not too sure about this way, but try it and see if it works for you!(11 votes)

- So regrouping and borrowing are the same thing?(6 votes)
- Yes they are the same thing.(8 votes)

- Is there a video for subtracting a bigger number from a smaller number? I need a little help with my homework...(6 votes)
- Hi Miraculous Ladybug,

When subtracting a bigger number from a smaller number, something like this should be seen:

5-7 = ?

When a bigger number is subtracted from a smaller number, the value that you get from that equation will be*negative*.

A number line looks something like this:

<*__l___l___l___l___l___l___l___l___l___l___l___l___l__*>

-3 -2 -1 0 1 2 3 4 5 6 7 8 9

When you subtract seven from five, you're subtracting seven "ones" from five, which will lead to negative two.

Hope this helped, and good luck on your math!(9 votes)

- Can we borrow if we have an equation like this? 367

-635 = ?(7 votes)- No since you are taking away more then what you have. In this case subtract 635-367 and make the answer negative. The answer is = -268. Negative means your answer is less than zero.(5 votes)

- The way i learned it you just add a small 1 above and slightly to the left of the digit,

but crosses out the number and rewrites it above with the borrowed digit. Is any one way right or better than the other?(5 votes)- There is no better way, but one way might be easier or simpler too you. Use whichever one you like most.(6 votes)

- What do I do if the tens place, the bottom number is bigger?(3 votes)
- you borrow so if you have 40-12 you would do 40

-12

0-2 you cannot do so you take off 1 from the 4 so it is 3 and give it to the 0 so it is a 10 and 10-2 = 8

so you have 3 10

-1 2 then do 3-1=2

2 8

so you get 28 i hope this helps(9 votes)

- What is regrouping? I don't fully understand the concept in the video.(3 votes)
- Regrouping is when a number is bigger than the number you are subtracting by and you have to borrow. One example is 46-38. 6 is less than 8 but the whole number is bigger. Then because of this you will have to borrow one from 4 and make the 6 a 16. This means you are taking ten away from the 4. Now the number becomes 316. The `16 stands in the place where the 6 used to be. You then do 16-8 and 3-3. Your final answer will be 8(9 votes)

- Can you say, "thirteenth tens?"(6 votes)
- If you are referring to the problem in the video, the 13 is in the ones column, not the tens.

So, it is thirteen ones, not thirteen tens.(2 votes)

- In the demonstration 83

-25

80 +3

20 -5

Why is 25 written as 20 - 5 and yet 25 is the product of 20+5?(3 votes)- If you look closely, you will see that it is -20 - 5 rather than 20 - 5. If you see a negative number being subtracted from another negative number, you will add the two negatives instead of subtract them. For example:

-20 - 5 = -25 -18 - 11 = -29 -4 - 3 = -7 -2 - 29 = -31 -6 - 6 = -12

Also, the problem was 83 - 25, so you can be assured 25 was negative.(2 votes)

## Video transcript

- [Voiceover] So let's see
if we can subtract 25 from 83 or if we can figure out
what 83 minus 25 is. I encourage you to pause the video and see if you can work through it. So I'm assuming you've had a try. And when you try to work through it, you probably first went to the
ones place right over here. And you probably said, "Hey,
I have three ones on top "and from that I want
to subtract five ones." But you said, "Wait, I can't subtract "five ones from three ones. "Five is more than three. "What do I do?" And what you do is what
I'm about to show you. You do something called regrouping. You take some of the value
that's in the tens place and put it into the ones place. What am I talking about? I'm gonna do it three different ways. So you really hopefully
understand what's going on. Well, you want this three to be more ones. You want it to be at least
as large as five or larger. So how do you do that? Well you could take a
10 from the tens place. So instead of having eight tens here, you could take one of them away and then you're going
to have seven tens here. And then if you take a 10, you could just put 10 away from here. You put in the ones place,
that's going to be 10. So 10 plus three is 13. 10 plus three is 13. So what did I do again? 83 is eight tens and three ones. You could also think of it
as seven tens and 13 ones. And I'm going to do it again in a couple of different ways to make that clear. But let's just work through this now because now you have
13 ones minus five ones which is going to be eight ones. And then you go to the
tens place and you say, "Seven tens minus two tens, "well that's going to be five tens." So your answer is going to be five tens and eight ones or 58. Now I said I would do this several ways so that it makes a little bit
more sense so let's do that. So another way that you could write 83 is you could write this, this is the same thing as 80 plus three. 80 plus three. That's the same thing as 83. Eights tens, three ones,
eight tens, three ones. And 25 is the same thing as 20 plus five. 20 plus five. Now we're going to subtract 20 plus five. So let's write this instead as... We're going to subtract 20. We're going to subtract two tens and we're going to subtract five ones. So subtracting 25 is the same thing as subtracting 20 and
then subtracting five. So now let's try to work
through it just like we did. Well we go to the ones place again. Ones again was a five. If I want to take five away from three, that's hard, I don't know
how to do that just yet. But what if I take ten from here? So if I take a 10, if
I take 10 from there, that's going to be 70. And if I put that 10 in the ones place, well 10 plus three is going to be 13. Notice, I haven't changed
the value of the numbers. 70 plus 13 is the exact same thing as 80 plus three which is 83. But what's useful about this is now, in the ones place, I can
subtract five from 13. If I subtract five from
13, I'm gonna get an eight. And then if I subtract
two tens from seven tens or 20 from 70, I'm going to get 50. I'm going to get 50. So this is going to end
up being 50 plus eight which is the exact same thing as 58. Five tens and eight ones. Now I said I would do the third way. And these are all the same way. I'm just writing it
down in different ways. So I could also write 83. I could write this down as eight tens plus three ones. All right, this is the tens place. This is the ones place. Eight tens, three ones. I'm gonna subtract two tens and five ones. So I could write... So this is going to be minus two tens and minus three ones. I'm sorry, and minus five ones. Minus five ones. 25 is the same thing as 20 and five. If I'm subtracting 25,
that's the same thing as subtracting 20 and
then subtracting five. And that's the same thing as subtracting two tens and then subtracting five ones. Two tens and five ones. So let's then work this out. So this is going to be... Well, as soon as we try
to subtract five ones from three ones, we say,
"It doesn't make any sense." Let me make the value here larger. And I'm gonna do that by
regrouping from the tens place. Instead of writing this as eight tens, I'm gonna take one of those tens away. I'm gonna write it as seven tens. And then put that 10 in the ones place. Well one 10 is equal to 10 ones. So if I added it to the three,
this is going to be 13 ones. And now I can subtract. 13 ones minus five ones is eight ones. And seven tens minus
two tens is five tens. Five tens. We are done. These are all different ways of doing the exact same problem with regrouping.