Arithmetic (all content)
- Relate place value to standard algorithm for multi-digit addition
- Multi-digit addition with regrouping
- Multi-digit subtraction with regrouping: 6798-3359
- Multi-digit subtraction with regrouping: 7329-6278
- Multi-digit subtraction with regrouping twice
- Alternate mental subtraction method
- Adding multi-digit numbers: 48,029+233,930
- Multi-digit addition
- Relate place value to standard algorithm for multi-digit subtraction
- Multi-digit subtraction: 389,002-76,151
- Multi-digit subtraction
Sal subtracts 6798-3359 using regrouping. Created by Sal Khan.
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- why do we borrow?(8 votes)
- We can't take away an 9 from an 8 and be left with a whole number, so we borrow a ten from the tens place. A 1 in the tens place is worth ten and a 1 in the ones place is worth 1, so when we borrow a 1 from the tens it shows up as a 10.(5 votes)
- I still don't get 6798-3359=? Does anyone else not get it . I just don't know how to regroup 8 and 9. Saul khan makes it sound so easy I wish I could be him, don't you?(3 votes)
- Why don't you spread it out the way Sal did.
You can take 10 from the 90 and bring it to the 8 to make 18. 18-9 is 9 so now you would be able to subtract it like this:
From there it is simple.(1 vote)
- my addition section wont let me complete it without wathing every single vidio but that is taking up my time of learning things that i need to now cause i already know how to do addition and subtraction i should be on algebra 1. does it matter if i mater the whole section. or will it not let me move on?(2 votes)
- If you can pass the Mission Challenges, for each Grade level, then you can move on to the next, or you can skip straight to the Course or Grade level you want whenever you feel ready, unless your progress is being controlled/directed by a teacher/coach.
The video lessons are here to help you with anything you don't already understand, but you don't have to watch them. You also have the option of watching them out of order, as you find that you need to refer to them, or watching them more than once if you have trouble with a concept. You can even click a link to a video from within the practice exercises or mission challenges that relate to that lesson.
KA makes it possible for you to learn math your way in your time - however and whenever you're ready to try. Good luck!(1 vote)
- Some one said that 1+1is not2,it's another number, is that true?(1 vote)
- Uh.. no, that person is wrong. You should check on a calculator next after somebody says something as dumb as that. XD(1 vote)
- why do we have to see it as hundreds. Can't we just see it as the combination why do we have to see it as hundreds it is just weird to me and makes no sens i wish that there was a better way to teach it plus it does not even make sens well i hope some one can answer this thx(1 vote)
We've got 6,798 minus 3,359. So let's see how far we can get with the subtraction. So immediately, when we go into the ones place, we're going to try to subtract a 9 from an 8. So we immediately reach a little bit of a stumbling block. And to see what our options are here in terms of regrouping, I'm going to rewrite both of these numbers. So I'm going to rewrite 6,798 literally. So this is equal to 6,000. That's this right over here. That's 6,000, plus 700, plus 90, plus 8. Minus all of this. So I could subtract each of the places. So I could say this is going to be minus 3,000 minus 300 minus 50-- a 5 in a tens place is just 50-- minus 9. So here, we're just explicitly showing what those place values represent. A 6 in the thousands place is 6,000. A 3 in the hundreds place is 300. Let's go back to our problem. We wanted to subtract a 9 from an 8. Well, that's a little bit of a stumbling block. But what if we could take some of the value from some of these and give it to the 8? In particular, we could go one place value up to the 90. And what if we were to take 10 from the 90? So let's do that. If we were to take 10 from the 90, then 90 becomes 80. But we don't want to change the value of the entire number. So we're going to give that 10 to this 8. We're essentially regrouping right over here. And then that 8 can become an 18. Notice, I did not change the value of the number. I just essentially changed how I represented it. Instead of saying it's 6,000 plus 700 plus 90 plus 8, I'm just saying that it's 6,000 plus 700 plus 80 plus 18. Those are both going to give you 6,798. But now it becomes a little bit easier for us to actually subtract. Now, if we subtract, I have 18 minus 9, which is 9. I have 80-- not 90, now. I have 80 minus 50, which is 30. And these are all positive, so this is plus 9. This is a positive 30. 80 minus 50 is 30. I have 700 minus 300, which is 400. And I have 6,000 minus 3,000, which is 3,000. So this is literally going to be 3,000 plus 400 plus 30 plus 9, or 3,439. Now, how would you do it if you didn't want to write it out like this? And this is where you'll see a kind of shorthand notation. This is often called borrowing. So you say, look, I've got an 8 in the ones place. I want to take a 10 from this 90. So it's going to become an 80. But we'll just write it as an 8 because it's in the tens place. This 8 represents the 80. And I'm going to give that 10 to the ones place. So 10 plus 8 is 18. And now you can subtract. 18 minus 9 is 9. 8 minus 5 is 3. 7 minus 3 is 4. 6 minus 3 is 3-- 3,439.