yego.me
💡 Stop wasting time. Read Youtube instead of watch. Download Chrome Extension

Subtracting a 1-digit number with regrouping | 2nd grade | Khan Academy


2m read
·Nov 11, 2024

  • So we have the number 35, which is 3 tens, because we have a 3 in the tens place, so we have 3 tens, and we have a 5 in the ones place. So, this is the ones place, I'll do the ones place in that same purple color. This is the ones place, and we see it represented here as 5, as 5 ones. So 35 is the same thing as 3 tens and 5 ones. 3 tens and 5 ones.

Now, what we wanna do with this video is subtract 8 from 35, and I encourage you to pause the video and try to figure out what 35 minus 8 is. Alright, so let's think about it. We have 5 ones, and we wanna take away 8 ones from there. Well, we don't know how to take 8 ones if we only have 5. We could take away 5, but then we're all out of ones, so how do we take away 8?

Well, this is where regrouping is valuable, because we don't only have 5 squares. We actually have 35 squares. We have 3 groups of ten squares, and then we have the 5 ones. So what if we were to take one of these groups of ten, right now it's in the tens place, and we were to regroup it into the ones place?

So let's say we were to take this group right over here, if we were to take this group of 10, and instead of expressing it in the tens place, let's put it in the ones place. So let's move it over here, and in the ones place, it would be, so 1 ten is the same thing as 10 ones, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10.

So what just happened there? I took away one of the tens, so now I only have 2 tens, and I took those 10 and put them in the ones place. So I have the original 5 ones, and then I have the new 10 that I just took from the tens place. So 5 plus 10 is going to be 15, so I now have 15 ones.

And now I can take away 8. So, if I take away 8 now, I would take away 1, 2, 3, 4, 5, 6, 7, 8, just to be clear. I'm taking away 8. And so what am I going to be left with? Well, I'm gonna be left with 2 tens, I'm gonna be left with 2 tens, and how many ones? I have 1, 2, 3, 4, 5, 6, 7 ones. 7 ones right over here.

Now how do we do it if I didn't wanna draw all of these things? Well, you would've said: Alright, I have 3 tens and 5 ones, this is where we started, but I took one of those tens, I took one of those tens away so I only have 2 tens now, and I took that group of 10 and put it in the ones place, so it's 10 ones.

So the 5 ones, plus another 10 ones, give us 15 ones. 15 ones. And so you can say I have 15 ones minus 8 ones is 7 ones, which we see over here, 1, 2, 3, 4, 5, 6, 7, so after doing the subtraction, we have 7 ones, and then I'll have 2 tens left in the tens place. So 2 tens, 7 ones. 27.

More Articles

View All
Brave New Words - Supt. Buffington, PhD, Tim Krieg, PhD, & Sal Khan
Hi everyone, s here from KH Academy and as some of you all know, I have released my second book, Brave New Words, about the future of AI in education and work. It’s available wherever you might buy your books. But as part of the research for that book, I …
The Dark Secrets of the Manhattan Project
In 1946, a 41-year-old hairdresser named Janice Shot came to A Strong Memorial Hospital in Rochester, New York, to be treated for scleroderma. It were a connective tissue condition. She had escaped the violence against Jews in Belarus during the Second Wo…
15 Things Millennials Spend Money On That Are Worth It
Millennials have been getting a bad rap for their spending habits for years now, and we’re here to bust some myths about it today. Now sure, we keep hearing that the avocado toast-loving, custom coffee-drinking generation are lagging behind when it comes …
Multivariable chain rule intuition
So, in the last video, I introduced this multi-variable chain rule, and here, I want to explain a loose intuition for why it’s true, why you would expect something like this to happen. The way you think about an expression like this, you have this multiv…
15 Costliest Mistakes Billionaires (and YOU!) Make
Billionaires, they’re actually just like you. You’re one successful adventure away from claiming it, and they are one big mistake away from losing everything. We all make the same mistakes, but the bigger your bank account, the harder your fall. So, you s…
Exploring Dog-Human Communication
What if you could communicate with your pet? If they could just tell you how much they love you, how when you leave the house to go to work, it feels like they’ve just spent a week without you? In the 1970s, a gorilla named Koko learned sign language. Wi…