# Second Grade - Lesson 6.7 Three Digit Subtraction

## Math

Hi, my name is Lisa Wong, and I'm a second grade teacher at PS101 in Brooklyn. Today, I will be teaching you the three digits of subtraction strategy, when we regroup hundreds and tens. I'm going to teach you the strategy of how to draw it out and also just using the basic vertical subtraction strategy in which we could open value. So let's read the problem together first. Jesse built two towers. She used 259 births for the first tower. She used 536 bricks in all. For which tower edition used more bricks. So if I'm teaching my students, I would always tell them to either take a colored pen, pencil or a highlighter, and circle key numbers that we need to use. So in this problem we will need, numbers 259, and 536 bricks. That's what we're working with. And then I would take another colored highlighter or a pencil, and I will underline the key question that they're asking and what we're trying to find. So it says, for which tower did she use more bricks? Enjoy that? And based on the keywords he was more. I know that we're trying to find a difference, and therefore my operation is subtraction. So you notice in a lot of the go math workbooks and textbooks, they set up the problem. With these lines, in boxes, above the number. The lines are there to help the students line the numbers all by place value. That way they don't get confused. You know, subtract the wrong digit with each other. And the bosses are there for regrouping. So let's set up this problem. I'm going to use a different color. So we need, when we subtract, we always put the bigger number first. So much of 36. -259. I'm going to draw a quick pick on the side. And this helps us solve this problem, especially when we have to regroup. So right away, I'm going to draw a quick pick of the 536, because that's what we are working with. And that's what we're subtracting. So when we draw hundreds, we draw boxes. Or what we call flats. One flat has ten tens. So we have 500, tens I usually just short longs or sticks. So three, 30, and 6, I destroyed dots or cubes. I was easier. So when I look at the ones column, only solving the ones called is first. I noticed that Ali has 6 ones. And I need to take away 9, so obviously I don't have enough. This is where I would regroup. So I would take another color. And I would borrow from the tents. And that's when I'm going to cross one out over here. And the tens will be dispersed into the ones, because we're regrouping them. One, two, three, four, 5, 6, 7, 8, 9, ten. Now we have enough. So when we add that ten in. The cross it out and the 6 becomes 16. Now we can subtract 9. So 16 minus sign. Of course not one, two, three, four, 5, 6, 7, 8, 9. And I'm going to count my remaining one, two, three, four, 5, 6, 7. Just bring down the 7 here. And also, when you cross out the tens, what we forgot to do, what we should have done is right and how many times we upload, which was two. But if you do it later on, it's fine as long as you notice it. Before you begin the subtraction for the tens place. So right away we know that we can't subtract 5 tens from two tens. So we're going to have to regroup again. So we did before we're going to cross out from the next column, which is the hundredths place. And a little bit across out over here. Now we have 400 slept. And then we're going to regroup to the Thames, so there's ten tens in 100, so we're going to draw it out. One, two, three, four, 5, 6, 7, 8, 9, ten. Now we have 12. So 12 -5 we can do. 5, one, two, three, four, 5, and let's we have left. One, two, three, four, 5, 6, 7. I'm going to bring that down here. And then we can do four minus two. There's enough. Now we're not done. We have to draw out the problem. So if we're talking about towers, I was sure a quick diagram of the towers. So the first house you used 259. Bricks. And we found out how many bricks you used in the second one which was 277. And we notice that 277 is greater than 259. Therefore, to find the correct answer, we will need to write out that the second tower added more bricks. So if we had a answer on the side, we would write that out. Try and use a different color. So the answer would be. Second. Tower. Or tower number two, or tower B, whichever one is in the problem. I hope this strategy helped you subtract three digits when regrouping hundreds and tens. Thank you for watching.