# Lesson Video: Adding Two-Digit Numbers with Regrouping Mathematics • 1st Grade

In this video, we will learn how to add a two-digit number to a two-digit number when crossing a ten and model this with place value equipment.

08:47

### Video Transcript

In this video, we’re going to learn how to add two two-digit numbers with regrouping and model this with place value equipment. The numbers 29 and 34 are both two-digit numbers. The two in the number 29 is worth two 10s, and the nine digit is worth nine ones. The three digit in the number 34 is worth three 10s, and the four digit is worth four ones. So when we’re adding two two-digit numbers, we have to add the tens and the ones.

When we’re adding two two-digit numbers, we always have to add the ones first. We need to add together the nine ones from the number 29 and the four ones from the number 34. The first thing we need to ask ourselves is, can we make a group of 10? Yes, we can. Nine plus one more makes 10. We have 13 ones altogether, a group of 10 and three more. When we can make a group of 10 ones, we have to regroup them and swap them for one 10.

Now we’ve finished adding the ones, we need to add the tens. 29 has two 10s, and 34 has three 10s. We already know we’ve got three ones. Let’s count the total number of tens. There are six tens blocks, which are worth 60. 60 plus three gives us a total of 63. 29 plus 34 equals 63.

First, we added the ones. We checked if we could make 10. We had 13 ones, so we were able to regroup 10 of our ones to make a tens block. Then, we added together the tens. Then, we put the tens and ones back together again. 60 plus three gave us a total of 63.

Let’s remind ourselves of the steps we need to make when we’re adding two two-digit numbers. First, we need to add the ones. Then, we need to check if we can make any tens. If we have more than 10 ones, we can regroup. Regrouping means making a group of 10 ones and swapping them for one 10. Then, we add the tens. Then, we add the total number of ones and the total number of tens together.

Let’s practice what we’ve learned by answering some questions now.

Using the given model, find 28 plus 46.

In this question, we’re adding two two-digit numbers. The number 28 has two 10s and eight ones, and the number 46 has four 10s and six ones. Let’s use a place value chart to help us add. When we’re adding two two-digit numbers, we always start by adding the ones. 28 has eight ones. 46 has six ones. Eight ones plus six ones gives us a total of 14 ones. We need to regroup 10 of our ones and make one 10. Our 14 ones make a group of 10 and four ones.

Now that we finished adding the ones and regrouping, we need to add our tens. 24 has two 10s, and 46 has four 10s. We’ve got seven 10s altogether and four ones. Seven 10s are worth 70, plus four ones make 74. 28 plus 46 equals 74.

Find the sum of 35 and 15.

When we see the word sum or the phrase find the sum, we know that means we need to add. We have to find the sum of our two two-digit numbers. The number 35 has three 10s and five ones, and the number 15 has one 10 and five ones. And this has been modeled for us in our place value table. When we add two two-digit numbers, we always have to add the ones first. Both of our two-digit numbers have five ones. What is five plus five? Five plus five is 10.

If the ones total 10 or more, we have to regroup. We can make a group of 10. And then we can swap our 10 ones for one tens block. So now we have a total of no ones. And we’ve got an extra 10 to add with the rest of our tens blocks. We know that 35 has three 10s and 15 has one 10. Three 10s plus one more 10 gives us a total of four 10s, plus the 10 we regrouped gives us a total of five 10s. Five 10s are 50. So 35 plus 15 equals 50.

First, we added the ones. We had 10 ones, so we regrouped. Then we added all our tens. There were five 10s. So 35 plus 15 equals 50.

Find the sum. 27 plus 33 equals what? Hint: Draw place value blocks to help you.

In this question, we have to add together two two-digit numbers. Each number has an amount of tens and ones. And we’re told to use place value blocks to help. We can model the number 27 using two tens blocks and seven ones. And we can model the number 33 using three 10s and three ones. Let’s start by adding the ones. There are seven ones in 27 plus three more ones in 33. Seven and three makes 10. We need to regroup these 10 ones and make one 10. Now we have no ones, and we’ve made an extra 10. Next, we need to add the tens. 23 has two 10s. There are three 10s in 33. Two 10s plus three 10s makes five 10s, plus the 10 we made from the ones. Altogether, we have six 10s. Six 10s make 60. The sum of 27 and 33 is 60.

What have we learned in this video? We have learned how to add two two-digit numbers with regrouping. We learned that first we add the ones and regroup. Then we add the tens.