Arithmetic (all content)
Learn to use regrouping to add 536+398. Created by Sal Khan.
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- Why is it that you can only "carry the one" and never "carry the two"?(172 votes)
- Good question. When you add two numbers, you are adding pairs of digits, as in the video. Those pairs can never add up to more than 18, (or 19 when you are carrying 1) .
But if you are adding three or more numbers, the digits you add together can add up to more than 18, in which case, you might have to carry two, three, or more.
Let' s try 276 + 499 + 387
2 Two units
2 Carry two tens
62 Six tens and two units
2 Carry two hundreds
1162 One thousand, one hundred, six tens and two units(190 votes)
- What if you were adding in the ones place and you had to carry 100
(Or a 1000 in the situation of the ten's place, and so on)?(7 votes)
- This might be an example of the situation that you're asking about.
To add these two decimals, the 3+9 = 12. Write a 2 in the ten thousandths' place. Carry the 1.
Then 9+0+1 = 10. Write a 0 in the thousandths' place. Carry the 1.
Then 9+0+1 = 10. Write a 0 in the hundredths' place. Carry the 1.
Then 9+0+1 = 10. Write a 0 in the tenths' place. Carry the 1.
Then 9+0+1 = 10. Write a 0 in the units' place and a 1 in the tens' place.
Final answer after all that carrying:
- Why can't you "carry the two"(3 votes)
- You can carry a 2. Lets say you were asked to add 19 + 9 + 39, while you are adding all the numbers in the ones column you would get 9 + 9 + 9 which equals 27. In this case you would write the seven and carry a 2 instead of a one over to the tens column. Now in the tens column you would add 2 + 1 + 3 which equals 6. Notice the 2 is from the 27 you carried over from the ones column. So your answer to 19 + 9 + 39 would be 67.(4 votes)
- I have two boys with special needs (FAS/FAE), one of which is having a difficult time understanding carrying over to the tens/hundreds. Your video does an excellent job for my other son and he understands the concept. Are there any other methods/techniques to introduce this concept of carrying over?(3 votes)
- You can always try a visual approach like with objects in the real world. When I was smaller I learned better with a visual that I could touch and interact with. Some examples of items you could use are candy, tokens, fruits (just things around the house, honestly). I hope this helps!(3 votes)
- From0:10to2:29why do you put it in expanded form?(3 votes)
- The expanded form is what explains why carrying works.
Here's an example:
286 = 200 + 80 + 6
+148 = 100 + 40 + 8
6+8 is 14 which is equal to 10 + 4. the unit digit is 4 we "carry" the 10.
now we have 10 + 40 + 80 = 130 which is equal to 100 + 30. 3 is the tens digit. We "carry" the 100.
and finally, 200 + 100 + 100 = 400, so the hundreds place has the digit 4
The answer is 434(3 votes)
- Why do you use the expanded form when you can use subtraction to check?(3 votes)
- The teachers want you to know exactly how you found what you found and so you know how to do it if you have a bit of trouble, and this is third grade work...they want them to show it.(2 votes)
- Why is it that you can only "carry the one" and never "carry the two"?(3 votes)
- Your answer cannot go above 20 to carry the two that means the answer is 20 to 30. You can only carry the one. For example, the highest 1 digit problem is 9 + 9. you can only get 18 and you have to carry the one.(2 votes)
- What if you r adding negative and positive numbers?
- In your example, -3+45 is the same thing as subtracting 3 from 45. so, -3+45 = 45-3 = 42.
-7+5 is the same thing as subtracting 7 from 5. -7+5 = 5-7 = -2.(1 vote)
- Why do you have to carry instead of just finding a different way? The carrying is complicated.(2 votes)
- You dont have to carry, but it actually makes things a lot simpler, when you learn, practice and understand it. But of course, if you want to find another way, go ahead! As long as you can work out the problem correctly, it doesn't matter how you do it!(3 votes)
- let's say we are answering this question 68+15 why when you get 13 you don't just put the whole number at the bottom. Why do you have to carry?(2 votes)
- You carry the 1 from 13 to make it easier to write. 5+8=13, 60+10=70, and 13+70=83. That works perfectly if you are doing the math in your head, but you carry the one so that on paper, you can add all of the tens at one time and avoid the extra step of adding 70+13.(3 votes)
Now, let's do the exact same addition problem that we did in the last video. But I'm going to expand out these numbers so that we really understand what's going on when we're doing all of this carrying. So this 5 is in the hundreds place. So it really represents 5 hundreds or 500. 3 represents 3 tens because it is in the tens place. So it represents 30. And the 6, well, it just represents 6 ones or 6. Likewise, this 3 represents 300. This 9 is 9 tens or 90. And this 8 just represents 8 ones or 8. And now we can add these two up. Now let's start in the right-most column-- this ones column. 6 plus 8, we've already figured out, is equal to 14, which is the same thing as 10 plus 4. So let's write the part that's not a multiple of 10 in this ones column. So let's put that 4 there. And the part that is a multiple of 10, we can now carry into this tens column. And that's just to keep track of it-- just to make sure that we don't lose that 10, we're putting it into the tens column. Now we can add all the tens. 10 plus 30 plus 90, we've already figured out is 130. Well the part that is not a multiple of 100, we can write in this tens column-- so the 30 part. And then the part that is a multiple of 100, we can put in the hundreds column. So we could put the 100 right over here. Notice, we've just carried the 1. But essentially, we've carried 100, because we put a 1 in the hundreds place. 10 plus 30 plus 90 is 100 plus 30. This is equal to 100 plus 30. That's all we've done. Now we can add the hundreds. 100 plus 500 plus 300 we've already figured out is 900. So we can write it as 900. And we're done! We've figured out that 500 plus 30 plus 6, plus 300 plus 90 plus 8, is equal to 900 plus 30 plus 4, which is the same thing as 934. So hopefully this gives you a little bit more sense of what we're doing when we "carry the 1" every time. 6 plus 8 is 14. We carried the 1. That 1 represents 10. It represents this 10 right over here. Just so we don't lose track of it. Then we say that 10 plus 30 plus 90 is equal to 130. So that's 30 plus 100. Then we add the hundreds together and we get 900.