Intro to subtraction with 2-digit numbers
- 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.