Video: Column Addition of Two-Digit Numbers

In this video, we will learn how to add two-digit numbers and record the calculation and any regrouping in columns using the standard algorithm.

12:37

Video Transcript

Column Addition of Two-Digit Numbers

In this video, we’re going to learn how to add two two-digit numbers using the column method. Here are two two-digit numbers, 27 and 45. The tens digit in the number 27 is a two. 27 has two 10s. We can model this using place value blocks. And the tens digit in the number 45 is a four. We can model this using four 10s blocks. Two 10s are worth 20. Four 10s are worth 40.

Two-digit numbers also have a ones digit. The ones digit in the number 27 is a seven. We can model the seven ones in 27 using seven ones blocks. And the five digit in the number 45 is worth five ones. We’ve modeled this using five ones blocks.

When we add two numbers using column addition, we write the numbers on top of each other. We add the ones first and then the tens. Let’s start by adding the ones in the ones column. We already know that 27 has seven ones and 45 has five ones. Here’s our seven ones from the number 27. And we can add the five ones from the number 45. How many ones do we have altogether? Seven plus five makes 12. Can you spot the deliberate mistake? We can only write one digit in the ones column. Once we reach 10 ones, we have to exchange them for one 10s block. So we have two ones in the ones column. And we have to write the 10 that we’ve exchanged in the tens column. We’ve written it in the square above our two 10s and our four 10s to help us remember to add this when we come to adding the tens column.

Now that we’ve finished adding in the ones column, we need to add the 10s. 27 has two 10s, and the number 45 has four 10s. Two 10s plus four 10s gives us a total of six 10s. But we have to remember to add the 10 we exchanged. Six 10s plus another 10 gives us a total of seven 10s. 27 plus 45 equals 72.

So, when we’re adding two two-digit numbers using the column addition method, first we write our numbers in columns. We always add the ones column first in case we need to regroup. And then we add the tens. Let’s try some questions now to help us practice adding two two-digit numbers using the column method.

Find 42 plus 29. Hint: Do you have to regroup ones to make a 10?

In this question, we have to find the sum of two two-digit numbers, the number 42 and 29. And we can see that the calculation’s been set out using the column method. We can see that 42 has four 10s and two ones. And we’re adding 29, which has two 10s and nine ones. We always start by adding in the ones column. We need to add two and nine. Two and nine is 11. But we can only write one digit in our ones column. We know that 11 is 10 and one more. So we write the ones digit in the ones column and one 10 in the tens column. 11 is one 10 and one one. We’ve exchanged 10 ones for one 10. And we’ve written this 10 above our other 10s to help remind us to add it to our other 10s when we’re adding in the tens column.

Now we can add the tens. We have four 10s in the number 42 and two 10s in the number 29. Four 10s plus two 10s gives us a total of six 10s. But let’s not forget we have another 10 which we’ve exchanged. Six 10s plus one 10 gives us a total of seven 10s. We added 42 and 29 to give us our answer of 71. First, we added the ones, and we had a total of 11. So we had to regroup 10 of our ones to make a 10. Then we added our 10s. We had six 10s and we added the one we’d regrouped, which gave us a total of seven 10s. 42 plus 29 equals 71.

Find the sum. Hint: Add the ones and then add the tens. 52 plus 17 equals what.

In this question, we have to find the sum of 52 and 17. And we’re given a hint. First, we have to add the ones, and then we have to add the tens. Let’s start by adding the ones. 52 has two ones, and the number 17 has seven ones. What is two plus seven? Two plus seven is nine. So we have a total of nine ones. Now we need to add the tens. 52 has five 10s, and the number 17 has one 10. Five 10s plus one 10 gives us a total of six 10s. The sum of 52 and 17 is 69.

Find the sum. Hint: Add the ones and then the tens. What happens when there are more than 10 ones? 54 plus 37 equals what.

In this question, we have to find the sum of two two-digit numbers, 54 and 37. We can tell by the way the sum has been set out that we have to use the column addition method. We have to start by adding the ones. 54 has four ones, and 37 has seven ones. Four plus seven gives us a total of 11 ones. And we know that the number 11 is made up of one 10 and one one. So we can write the one in the ones column. And we have to regroup 10 of our ones and exchange them for one 10.

In this calculation, we’ve written the 10 we’ve exchanged underneath the other tens. Sometimes we write this number at the top of the other tens. Wherever we write the 10 we’ve exchanged, we have to remember to add it when we’re adding in the tens column. Let’s add the tens. 54 has five 10s. 37 has three 10s. Five 10s plus three 10s gives us a total of eight 10s, plus the one we exchanged gives us a total of nine. Five plus three plus one equals nine. The sum of 54 and 37 is 91.

Chloe spilled ink on her homework. Find the covered numbers.

Chloe’s first sum is 28 plus another two-digit number. 28 plus something equals 89. And we can see that Chloe has spilled ink on one of the digits in her calculation. If we start by adding the ones, eight ones plus one one gives us a total of nine ones. What did Chloe add to her two 10s to give her a total of eight 10s? We know that two 10s plus six 10s gives us a total of eight 10s because two plus six is eight. So the missing digit in the tens column is a six. 28 plus 61 equals 89.

Chloe’s second sum has ink spilled on one of the ones digits. Thirty something plus 23 equals 58. So we just need to find the missing ones digit. What do we add to three to give us a total of eight? We know that three plus five equals eight. 35 plus 23 equals 58. So the missing digit is a five. Five ones plus three ones equals eight ones.

In Chloe’s last sum, two of the digits have been covered with ink. 64 plus what equals 79. Let’s start by thinking about the missing ones digit. 64 has four ones, and we have a total of nine ones. What do we need to add to four to give us nine ones? We know that four plus five is nine. So the missing ones digit is a five. Now let’s find the missing tens digit. 64 has six 10s, and we have a total of seven 10s. Six plus one equals seven. So the missing tens digit is a one. Six 10s plus one 10 equals seven 10s. So the missing number in this calculation is 15. 64 plus 15 equals 79.

We used the column addition method to help us find the missing digits. The missing number in the first addition is six, the second missing number is five, and the third missing number is 15.

What have we learned in this video? We have learned how to add two two-digit numbers using column addition. We’ve learned that first we add the ones column, and then we add the tens column.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.