Lesson Video: Column Subtraction of One-Digit Numbers from Two-Digit Numbers Mathematics • 2nd Grade

Video Transcript

Column Subtraction of One-Digit Numbers from Two-Digit Numbers

In this video, we’re going to learn how to subtract a one-digit number from a two-digit number and how to record the calculation and any regrouping in columns.

A class are having a craft fair. One of the students has decided to paint rocks. If she has 35 rocks and has already painted eight of them, how many rocks does she still have to paint? This is a subtraction problem. To find out how many rocks the student still has to paint, we need to subtract eight from 35. In this video, we’re learning about column subtraction. Let’s use this method to solve our problem. When we use the written method of column subtraction, we write the number that we’re subtracting from at the top, making sure that we put the tens digit in the tens column and the ones digit in the ones column. The student had 35 rocks, and we know that 35 has three 10s worth 30 and five ones.

So we know that we’ve written the digits in the correct column in our place value table. We need to subtract eight from 35 because the student has already painted eight of her rocks. And we’ve written our eight digit in the ones column. When we use the column subtraction method, we always start by subtracting the ones first. We already know that the number 35 has three 10s worth 30 and five ones. We can model our number using three 10s blocks and five ones blocks. Let’s start by subtracting the ones. We’ve got five ones in the number 35, and we need to subtract eight ones. Can you spot the problem? We don’t have enough ones. Five is less than eight, so we need to regroup.

That means we need to take a group of 10 or one of our tens blocks and add it to our ones. Now we have 15 ones. And we no longer have three 10s; we only have two 10s, which are worth 20. So we can cross out the five ones and write 15 ones instead. Now we can subtract in the ones column. 15 ones take away eight ones. Here we go. We’ve crossed out eight of our ones. We have seven ones left. Now we need to subtract in the tens column. We don’t have three 10s anymore. We have two. And there’s nothing to subtract from our two 10s. So 35 subtract eight equals 27. If a student has 35 rocks and has painted eight of them, she will have 27 rocks left to paint.

Let’s recap what we’ve learned about subtracting one-digit numbers from two-digit numbers using the column method. Step one: We write the calculation in columns. It helps to use squared paper to make sure that we write the ones digits in the ones column and the tens digits in the tens column. Step two: We subtract the ones, remembering to record any regrouping we have to do. And step three: Subtract the tens. Let’s practice what we’ve learned about column subtraction by answering some questions now.

Take away four from 65.

In this question, we have to subtract a one-digit number from a two-digit number. And we have to use the column subtraction method. The number we’re taking away from is 65, which has six 10s and five ones. And we have to subtract four from this number. Four is a one-digit number, so it just has a ones digit. So the calculation has already been written for us, which means we can start subtracting. And we always subtract the ones first. The number 65 has five ones, and we need to subtract four ones. This is quite an easy calculation. Five take away four equals one. Five ones take away four ones leaves us with one.

Now, all we need to do is subtract in the tens column. There are six 10s and nothing to subtract. This is because we’re subtracting a one-digit number from a two-digit number. Six 10s take away no 10s leaves us with six 10s. We didn’t need to do any regrouping. We had enough ones to subtract from. 65 subtract four is 61. When we subtract a one-digit number from a two-digit number using column subtraction, first, we have to write out the calculation. Then we subtract the ones, making sure to record any regrouping we need to do. Then we subtract the tens. 65 subtract four equals 61.

Take away eight from 42. Hint: Regroup one 10 into 10 ones.

In this question, we have to subtract our one-digit number, eight, from a two-digit number, 42. And we have to use the column subtraction method. The calculation has been written out for us. So we can start subtracting. When we’re subtracting using the column subtraction method, we always start subtracting in the ones column. 42 has four 10s worth 40 and two ones. We can model this number using four tens blocks and two ones blocks. So we have two ones and we need to subtract eight ones. You may have already realized we don’t have enough ones to subtract eight. Two is less than eight.

Luckily, the question has given us a hint. We’re told we need to regroup one 10 into 10 ones. This means we need to take one of our 10s and we group it into 10 ones. So now we have three 10s and 12 ones. We need to make a note of what we’ve done to our number. We can cross out our two ones and write 12 ones. And we don’t have four 10s anymore. We have three. Now that we’ve regrouped, we can subtract in the ones column. 12 ones take away eight ones leaves us with four ones. Now we just need to subtract in the tens column. Because we’re subtracting a one-digit number from a two-digit number, there’s nothing to subtract from our tens. Three 10s take away no 10s leaves us with three 10s. We took away eight from 42 using the column subtraction method. 42 subtract eight equals 34.

Find the answer to the following equation. 28 subtract six equals what.

In this question, we have to subtract a one-digit number, which is the number six, from a two-digit number, 28. And we have to use column subtraction. When we use column subtraction, we always start by subtracting in the ones column. Number 28 has eight ones, and we need to subtract six. What is eight subtract six? It’s two. Six plus two is eight. Eight subtract six is two. Now all we need to do is subtract in the tens column. 28 has two 10s and six has no 10s. Two 10s subtract no 10s leaves us with two 10s. 28 subtract six equals 22. We found the answer using column subtraction. First, we subtracted in the ones column. Then we subtracted in the tens column to give us the answer 22.

Perform the following subtraction. 24 subtract seven equals what.

In this question, we’re subtracting a one-digit number, which is the number seven, from 24, which is a two-digit number. And we’re using the column subtraction method. We need to start by subtracting in the ones column. 24 has four ones and we need to subtract seven ones. Now we have a problem. Four is less than seven. We don’t have enough ones to subtract from. We’re going to need to regroup. We need to regroup one of our tens into 10 ones. So instead of having two 10s, we’ll have one 10. And instead of having four ones, we’ll have 14 ones. So now we can subtract in the ones column. What is 14 subtract seven? 14 take away seven is seven.

Now all we have to do is subtract in the tens column. And because we’re subtracting a one-digit number from a two-digit number, there’s nothing to subtract from our one remaining 10. One 10 take away no 10s leaves us with one 10. 24 subtract seven equals 17. We used the column subtraction method to find our answer. First, we subtracted in the ones column. And we had to regroup one of our 10s into 10 ones. Then we subtracted in the tens column to give us our answer of 17.

What have we learned in this video? We have learned how to subtract a one-digit number from a two-digit number using column subtraction. We learned that we always subtract the ones first and record any regrouping. We also learned that after we subtract the ones, we subtract the tens.