Addition with regrouping | Addition and subtraction within 100 | Early Math | Khan Academy

Addition with regrouping | Addition and subtraction within 100 | Early Math | Khan Academy


– [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.

22 Replies to “Addition with regrouping | Addition and subtraction within 100 | Early Math | Khan Academy”

  1. Well, I enjoy your physics laws explanation videos but this one…I mean how else would you do it? I felt like attending primary school 😀

  2. I have learned how to multiply when I have written an assembler program to multiply.
    If you want to multiply two numbers that can have up to 256 digits each, how would you do that? for example 63768736782634762387682173687216371298743987398712983729817398172398712398972193871239873873219832131231236876128763187236243988768687687687621367123657635217652176576532167567125766567632981 X 90712903709123709172390712903798949879812378912739871289723598438723489793287498239482894789234768742356476491231289361273901720937120937910237091273091723907129037109273901273901270937912379 = ?
    I wrote an assembler program to do that, on a 6502 microprocessor. My program was very fast. The result could be a number with 512 decimals at most. I have used a multiplication table to do the multiplication of two numbers. Instead of adding numbers, I would just use a table, like 8 X 8 = 64. No need to compute it. I had a table whit two indexes that would tell me that 8 X 8 is 64. No need to add 8 times 8. My program was the fastest algorithm to multiply these numbers.
    I have got an A grade!

  3. U Was w USA edukacja musi stać na niskim poziomie, skoro dorosłym ludziom trzeba tłumaczyć takie proste rzeczy na Youtubie. U nas w Polsce ja się  takiego dodawania nauczyłem w I klasie szkoły podstawowej, gdy miałem 8 lat.

  4. We call it Carrying Numbers here in the UK and that is easier to remember it as that than "regrouping", easiest way to remember how to do this in Addition is when adding the Ones together if the total amount adds up to the number 10 or over then you Carry the 10 over to the top/left Tens place but it doesn't make it another Ten only Ones you're adding on :).

    A tricky one you might encounter at some point is:

    45
    +25
    ——–

    What would you do? write in the 10 as the total? or carry it over to the top/left Tens place?




    You'd still carry it over to the top/left Tens place and write in 0 underneath to make the total 70 because 45+25 is 70 🙂 if you wrote in the 10 in the total underneath then it would make it add up to 610 but that's NOT right because it should be 70. 4+2 is 6 but we need a total of 7 under the Tens place so you'd have to carry the 10 over to make it 1+4+2=7 😀

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