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### Course: Arithmetic (all content)>Unit 2

Lesson 10: Addition within 100

# Adding with regrouping

Sal adds 35 + 27 thinking about place value.

## Want to join the conversation?

• Im using this video to help my nephew with regrouping. he doesn't understand why you have to add the ones column first and refuses to add that way. he tends to add mentally which is great but needs to know how to do it out. Any tips on how to get him to add the ones column first and why its so important?
(15 votes)
• explain to him that when you add numbers that you need to add the smallest digit first so that your number isn't to small. try to make it fun so that he looks forward and listens. every time he does it the way he's supposed to give him candy Etc...
(12 votes)
• it's 62 right? because 5+7 is 12 and 4+2 is 6 right?
(3 votes)
• Yes, 35 + 27 evaluates to 62. You are correct.
(3 votes)
• Why is this called regrouping, and does it also apply to multiplication and division, not just addition and subtraction?
(4 votes)
• Regrouping because it groups the numbers together again. Like words like reload, redo, the re- prefix means 'again' so regrouping means group again. In a away, it the numbers do group again.
Regrouping doesn't apply to multiplication and division. Division has something like regrouping but I think it's called something different.
(2 votes)
• What is the relationship between adding and subtracting?
(0 votes)
• They're opposites! Adding increases number, while subtracting makes it smaller. For example; 15 + 10 = 25, 15 gets bigger when you add ten, but if you do 15 - 10 = 5, 15 gets smaller since you subtract ten.
(6 votes)
• I am using this for review before I get to math I actually add these in my head without grouping or anything else. Is this going to cause me a problem when I get to more complicated math?
(1 vote)
• If you do the problems in your head, make sure that your method gives correct answers. If your teacher asks you how you are doing the problems, be ready to explain your method.

If you are getting a lot of wrong answers doing problems in your head, then it’s better to change to using pencil and paper.

Have a blessed, wonderful day!
(3 votes)

## Video transcript

- [Voiceover] So I have two numbers here. The top number I have one, two, three 10's, and I have one, two, three, four, five ones. Three 10's five ones or 35. The second number here I have two 10's, one, two, and I have one, two, three, four, five, six, seven one's. Two tens and seven ones. Now what I want to do is I want to add all of these numbers. Well, I want to add these two numbers together. I want to add 35 + 27, or another way of thinking about it, I want to add, I want to add all of these blocks together, I want to add all of these blocks together. So, let's start, let's start in the ones place right over here. So I have five one's here. I have seven ones here. So if I add five ones to seven ones how many ones am I going to get? I'm gonna get 12 ones. I'm gonna get one, two, three, four, five, six, seven, eight, nine, 10, 11, and 12. Now you might notice a problem here. 'Cause if I take 5 + 7 I can't write the number 12 in just the ones place. I just need to have one digit. I can't have two digits there. So what can we do? Well, what we could do is take 10 of these ones and group them into a 10 and put them into the 10's place. What am I talking about? Well what we could do is, we could take one, two, three, four, five, six, seven, eight, nine, and 10. So we could take these 10 right over here and group them together into one of these bars. So let's do that. So let's group them together into one of these bars, and then stick that bar in the 10's place. So all I'm doing here... All I am doing here is, give me one second. Let's see, alright, whenever I... So all I'm doing is I'm taking these 10 right here, and I'm regrouping them into the 10's place. Sometimes this is called carrying. So instead of writing 10 one's I'm gonna write it as one 10. So instead of writing it as ten ones, I'm going to write it as one 10. So what does that do for us? Well now I only have two ones in the ones place. I only have two ones in the ones place, but now I have one more 10 in the 10's place, and I have one more 10 in the 10's place. Sometimes people call this carrying because you see 5 + 7 is 12. You write the two in the ones place and you write the one in the 10's place. Twelve is one, two. Let me make it very clear. 5 + 7 = 12, and all we did is we wrote the one here, we wrote that in the tens place. We wrote it up here so that's why it kind of looks like you are carrying it. You are putting it at a higher place, but you're just writing this in the 10's place. Up here was just an easy place to do it, but remember all we did, all we did there is we said "Look, we have five we have seven that would be 12." "We can't write a 12 in the ones place." "So, let's take 10 of those 12 and regroup them as a 10" and then we have the two left over here, but an easy way to think about it is 5 + 7 = 12, one, two. And now we can add the 10's place. We have one 10 plus three 10's plus two 10's. Well what's that going to be? Well that's going to be six 10's! 1 + 3 + 2 = 6. So let's do that. So we have, whoops wow that was... That's not what I wanted to do. Let me, that was kinda, alright. (laughs) We have one, we have two, we have three, and we have four, and we have... My computer is slowing down. Five, and we have six, six 10's. Six 10's and so what does that... What does that leave us with? One plus three plus two 10's is going to be six 10's. 35 + 27 = 62. 35 plus 27 is six 10's and two one's, 62.