If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:5:27

Video transcript

so let's see if we can subtract 25 from 83 or if we can figure out what 83 minus 25 is and 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 then 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 now I'm going to 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 it 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 ten because I just took a ten away from here you put in the ones place that's going to be 10 so 10 plus 3 is 13 10 plus 3 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 80 plus three eighty plus three that's the same thing as 83 eight tens three ones eight tens three ones and 25 is the same thing is the same thing as 20 plus 5 20 plus 5 now we're going to subtract 20 plus 5 so let's write this instead as we're going to subtract 20 we're going to subtract 2 tens and we're going to subtract 5 ones so subtracting 25 is the same thing as subtracting 20 and then subtracting 5 so now let's try to work through it just like we did well we go to the ones place again and once again with a 5 if I want to take 5 away from 3 that's hard I don't know how to do that just yet but what if I take 10 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 3 is going to be 13 notice I haven't changed the value of the number 70 plus 13 is the exact same thing as 80 plus 3 which is 83 but what's useful about this is now in the ones place I can subtract 5 from 13 well if I subtract 5 from 13 I'm going to get an 8 and then if I subtract 2 tens from 7 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 8 which is the exact same thing as 58 five tens and eight ones now I said I would do it a 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 8 tens eight tens plus three ones plus three ones all right this is the tens place this is the ones place eight tens three ones now I'm going to subtract two tens and five ones so I could write so this is going to be minus minus two tens minus two tens and minus three ones I'm sorry and minus five ones minus five ones 25 is the same thing as two as as 20 and five if I'm subtracting 25 that's 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 anyway that's not making any sense let me make the value here larger and I'm going to do that by regrouping from the tens place so instead of writing this as eight tens I'm going to take one of those tens away I'm going to write it as seven tens and then put that 10 in the ones place well ten 110 is equal to ten ones so if I add 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 10s minus two tens is five times five tens and we are done these are all different ways of doing this exact same problem with regrouping