Sal uses place value blocks to regroup and subtract 438-272. Created by Sal Khan.
- [Instructor] What we want to do in this video is figure out what 438 minus 272 is and to help us think about that we have these place value blocks right over here. So you can see 438. We have four hundreds, 100, 200, 300, 400. We have three tens, one, two, three and then we have eight ones. You can count those eight ones right over there. From that, we're going to take away two hundreds, so that's 200 right over there, seven tens or 70 right over here, and two ones. So pause this video and see if you can figure out what this is going to be. All right. Now let's work through this together. So first of all, we could start in the ones place and we can see we have eight ones and then we're gonna take away two ones. So that's pretty straight forward. We're just going to be left with six ones right over here. Now let's go to the tens place. Now the tens place is interesting. We have three tens here and we're trying to take away from that one, two, three, four, five, six, seven tens. So how do you take seven tens from three tens? Well, luckily we can regroup from the hundreds place. What if we were to take this piece right over here from the hundreds to the tens place and now this is going to be the equivalent of 10 tens. So let me represent it that way. Once again, I took a hundreds. That's the same thing as one, two, three four, five, six, seven, eight, nine, 10 tens. Well, this is useful now, because now I have 10 plus three tens, or you could say I have 13 tens and now I can take away seven tens from that. So let's do that. Let's take away one, two, three, four, five, six, seven and what we are left with is six tens right over here. So now I have six tens left, six ones left and in the hundreds, I have three hundreds. I'm gonna take away two of them. So I'm gonna take away 100 and 200. So I'm left with just 100 there. So I'm left with one hundred, six tens and six ones. So this is one hundred, six tens and six ones, or 166.