Lesson Video: Subtracting Ones from Teen Numbers: Subtracting From Ten Mathematics

Video Transcript

Subtracting Ones from Teen Numbers: Subtracting from 10

In this video, we’re going to learn how to subtract a one-digit number from a teen number by splitting the teen number up into a 10 and some ones and then subtracting from 10.

Now that we’ve got the title page out of the way, it’s time to let you into a little secret. Even though this video is called subtracting ones from teen numbers, even though we saw an example of a teen number on the title page, and even though all the way through this video we’re going to be seeing lots of teen numbers that we have to take away from, guess what? In this video, all we really need to know how to do is subtract from 10.

So whilst the question might be asking us to take away from a teen number, all we need to think about is taking away from 10. And this is great because subtracting from 10 is just so quick to do, because as long as we know pairs of numbers that go together to make 10, we can use these facts to help.

Seven and three make 10. So 10 take away three must leave us with the number that goes together with three to make 10. We’re left with seven. And if we want to know what 10 take away nine is, we just think of the number that goes together with nine to make 10. And we can see that the answer is one. And knowing that two and eight are a pair that go together to make 10 helps us to see straightaway that 10 take away eight leaves us with two. So subtracting from 10 is really quick.

And let’s see now how we can use it to help us when we have to work with teen numbers. Let’s imagine that we’ve been asked to find the answer to 16 take away seven. We could use 16 counters to help us here. 16 is one of these teen numbers that we’ve been talking about. It’s made up of a 10 and some ones. In fact, let’s split it up into a 10 and some ones. We could put 10 counters in a box. This helps us to see that 16 is made up of 10 and six more. And remember, we need to take away seven from this amount. Can you see a way to take away seven really quickly? Why don’t we take it away from this 10? Because, as we’ve said already, subtracting from 10 is really quick.

Can you think of the number that pairs with seven to make 10? Seven and three makes 10. And so if we take away seven from 10, we’re left with three. Now, remember, our question is all about subtracting from 16. So in order to find the answer, we’re gonna have to combine our two parts back together again. We have three counters left over here and those six ones that we separated at the start. And three plus six equals nine. And that’s how we know that 16 take away seven equals nine. And that’s why we said that in this video we’re going to be practising the skill of subtracting from 10. By splitting the number 16 into a 10 and six ones, we could take away the number we needed to subtract from the 10, which we know is really quick to do.

The only other thing we need to remember is to put the two parts back together at the end. Let’s try answering some questions now where we have to subtract a number of ones from a teen number. And each time we do, let’s look for the way that we can find the answer by subtracting from 10.

Which addition expression is equal to 14 subtract nine?

In this question, we’re given a subtraction to think about, 14 take away nine. Can you see it’s written underneath the question, too? But instead of finding the answer to 14 take away nine, this is a really interesting question. It says, “Which addition expression is the same as 14 take away nine?” In other words, what numbers can we add together that will be the same as if we had 14 and took away nine? Thankfully, we’ve got a picture of some counters here to help us. Now something’s happened to these counters. Perhaps it might be a good idea if we had some counters of our own and we see exactly what we’ve done to them to help work out 14 take away nine.

So to begin with, let’s take 14 counters. Now we need to take away nine counters from 14. And to help us do this quickly, we can split up the number 14 into two parts, because 14 is a teen number. We can split it up into 10 and four more. One 10 and four ones is the same as 14. Now, at the moment our four ones are in a bit of a square shape. But if we make them into a line and split them up, can you see that this is exactly the same as what we’ve got in our top picture? Now, why would we want to split up 14 like this? Well, remember, we need to take away nine counters. And because we know a lot of the pairs that make 10, it’s much quicker to take away nine from 10 than from 14.

So what our picture is showing us is that we can take away nine from 10. One, two, three, four, five, six, seven, eight, nine. We only have one counter left. Of course, you probably knew this before we started, didn’t you? We know that nine and one go together to make 10. So if we start with 10 and we take away nine, we’re going to be left with one. Now although we’ve found out what 10 take away nine is, remember, we needed to find out what 14 take away nine was. So to find the overall answer, we’re going to have to take this one here and these four counters here and add them together again. One plus another four equals five. And so we can say that 14 subtract nine leaves us with five.

So let’s go back to our question, although we know that 14 take away nine is five, remember, we were asked which addition expression is the same as 14 take away nine. Well, there are lots of additions that make five, but there’s only one that we’ve used in this question. Can you spot it? It was when we added our one remaining counter back together with our four counters. It was when we said one plus four equals five. The addition expression that we found that was the same as 14 take away nine is one plus four.

What is 14 subtract eight. Hint: Subtract from 10.

It looks like we need to take away a ones number from a teen number in this question. We need to subtract eight from 14. But wait a second. The hint that we’re given doesn’t say subtract from 14; it says subtract from 10. Why did it say this? It’s a bit strange. In the picture, we can see 14 counters that are being put into 10 frames. And this gives us a little bit of a clue as to what we need to do. Because by using 10 frames, we can see that the number 14 is the same as one lot of 10 and then four ones. So instead of taking away eight from 14, by splitting the number up like this, we can take away eight from 10.

And this is what the hint is really telling us. It’s really saying to us, don’t take away from the whole amount. Now that you’ve split up 14 into one 10 and four ones, just look at the one 10. It’s much easier to subtract from 10. And the reason it’s much easier and quicker to subtract from 10 is because all we need to do is to think of the pairs of numbers that go together to make 10. And because we want to subtract eight, all we have to do is think of the number that goes together with eight to make 10. Now, if we draw a line here on our 10 frame, we can see that eight and another two go together to make 10. So if we start with 10 and take away eight, we’ll be left with two.

Now remember, the calculation we’re trying to work out here is 14 take away eight. So to see how many counters we’ve got left, we need to add the two parts we’ve got back together again. And two plus four equals six. To find the answer to 14 take away eight, we first split up the number 14 into 10 and four. We did this because subtracting from 10 is much quicker than subtracting from 14 because we know all the pairs that go together to make 10. 10 take away eight leaves us with two. Then we had to put the two parts back together again. Two plus the four ones equals six altogether. And that’s how we know that 14 subtract eight equals six.

Fill in the blank: 10 take away seven equals what. And then fill in the blank: 15 take away seven equals what.

This question has two parts. And did you notice? They’re linked. In both parts, we need to take away seven. In the first part, we’re asked to start with 10 and take away seven. But then, in the second part, we need to find the answer to 15 take away seven. And why do you think we’re given two similar calculations like this one after another? Do you think maybe the first calculation might help us find the answer to the second? Let’s find out. Now there’s a reason why we don’t have a 10 frame to help us with this first question because taking away numbers from 10 is quite quick and easy to do. We just need to remember the facts we know about the numbers that go together to make 10.

Now do you remember what goes together with seven to make 10? We know that seven and three makes 10. And so if we start with 10 and take away seven, we’re going to be left with three. So if 10 take away seven equals three, how could we use this to help us find the answer to 15 take away seven. Well, this is where our 10 frames come in useful because they help us to see that the number 15 is made up of 10 and five ones. And so if we want to take away seven from 15 really quickly, we can just start by looking at this one 10 because we know how to take away seven from 10 really quickly. As we’ve said already, 10 take away seven is going to leave us with three.

So to find the answer to 15 take away seven, we just need to add the three ones that we’ve got left with the five ones over here. And we know that three plus another five equals eight altogether. And that’s how we know that 15 take away seven equals eight. We’ve used a fact to do with subtracting from 10 to help us take away from a teen number. 10 take away seven equals three. And so we know that 15 take away seven equals eight.

Subtract eight from 13. Hint: How can subtracting from 10 help you? 13 take away eight equals what.

In this question, we’re being asked to subtract or take away eight from 13. Sometimes, when we describe a subtraction like this using words, it can be easy to see the number eight before the number 13 and think that we might be talking about eight take away 13. Well, this isn’t right at all, and we need to think carefully about what the words mean. We need to subtract or take away eight from 13. In other words, we start with 13, and we take away eight from it. It’s just important to remember this because sometimes we see the numbers the other way round and we think that this is the way we need to write our subtraction.

So we need to find the answer to 13 take away eight. But we’re given a hint here. We’re asked how can subtracting from 10 help you? And underneath this question, we’re given a little clue to help us. We can see the calculation 13 take away eight. But we can also see that the number 13 has been split up into 10 and three. Now often, when we split up numbers like this, we put the larger number first. So you might be expecting it to look a little bit like this. But, you know, there’s a reason they’ve been written the other way around. And it’s all to do with how useful both parts are to us. Remember, we need to take away eight from this number. Can we take away eight from three or 10? Well, we know three is too small, isn’t it? But we can easily and quickly subtract eight from 10. All we have to do is think of the number that goes together with eight to make 10.

So in other words, although we split up 13 into two parts, the most useful part to us at the moment is this 10 here. And that’s why we’ve written it on the right-hand side so that it’s easier for us to see that we need to take away eight from it. Now what do we put together with eight to make 10? We know that eight and another two make 10. So if we take away eight from the 10 part of our number 13, we’re going to be left with two. But remember, our number 13 isn’t just made up of 10. It’s also made up of those three ones. So to find the overall answer, we’re going to need to take the two that we had left over after the subtraction and add those three ones. And we know that two plus another three equals five altogether. And so we can say that 13 take away eight must be worth five.

So in this question, we needed to find the answer to 13 subtract eight. And our hint asked us another question. How can subtracting from 10 help you? Well, how it can help us is that we can split up the number 13 into 10 and three. And because it’s much quicker to take away eight from 10 than from 13, we can work out this subtraction really quickly and then add the three back on. We know that 10 take away eight is two. And so 13 take away eight is just going to be three more than this. 13 take away eight equals five.

What have we learned in this video? We’ve learned how to subtract a one-digit number from a teen number by subtracting from 10 to help.