Lesson Video: Subtracting Ones from Teen Numbers: Making Ten Mathematics • 1st Grade

In this video, we will learn how to subtract a one-digit number from a teen number when we cross a ten by subtracting the ones in two steps.

10:07

Video Transcript

Subtracting Ones from Teen Numbers: Making 10

In this video, we’re going to learn how to subtract a one-digit number from a teen number when we cross a 10. And we’re going to do this by subtracting the ones in two steps.

Now, before we start, there are two things that are gonna help us here. The first thing is that we can subtract from a teen number to 10 really quickly. Let’s imagine that we have a teen number like 19. And we want to take away something so that we’re left with 10. Well, we just take away all the counters in this ten frame, don’t we? 19 take away nine is 10. 15 take away five equals 10. And what do we take away from 12 to take us to 10? Well, it’s the number two, isn’t it? So, the first skill that’s going to help us here is that we can subtract up to the number 10 really quickly.

And the second skill that’s gonna help us here is that we can subtract from the number 10 really quickly, too. Let’s imagine we need to take away two from 10. Well, to do this, we need to think about which number pairs with the number two to make 10. We know that two and eight go together to make 10. So, we can say really quickly 10 take away two leaves us with eight. To subtract from 10 really quickly, we just need to think of pairs that go together to make 10. Six and four make 10. So, if we take away six from 10, we’re left with four.

Now, we’re going to try subtracting some ones from some teen numbers. And we’re going to find the answer to questions like 17 take away nine by subtracting in two steps. In the first step, we’re going to subtract up to the number 10, which we know we can do really quickly. And you guessed it! In the second step, we’re going to subtract from the number 10. As we’ve seen, we can do this really quickly, too.

Let’s have a go at 17 take away nine.

Let’s imagine our friend the panda here has 17 bamboo shoots for his tea. Let’s put them in ten frames so that we can see what we’re doing. Now, let’s imagine another panda comes along and eats nine of his bamboo shoots. 17 take away nine leaves us with what? And one way we could find the answer is to start with the number 17 and to count back nine. But we know some quicker ways of subtracting.

We know that we can subtract to the number 10 very quickly. And we know that we can subtract from the number 10 very quickly. Instead of subtracting nine all in one go, what if we complete the subtraction in two parts? First, let’s subtract up to the number 10. What do we take away from 17 to get to 10? We know we can do this really quickly. We just need to subtract all the bamboo shoots in this ten frame.

We need to start by taking away seven because we know 17 take away seven leaves us with 10. So far, we’ve only subtracted seven out of nine. We need to subtract the rest now. Seven and another two make nine. So, now, we need to take away the remaining two. And again, we can do this really quickly because this time we’re subtracting from 10.

Remember how we subtract from 10? We need to think about which number pairs with the number two to make 10. We know that eight and two make 10. And so, in our second step, we can see that 10 subtract two leaves us with eight. And this is the number of bamboo shoots our panda has got left. 17 subtract nine equals eight.

Now, let’s have a go at answering some questions where we have to subtract ones from teen numbers. And each time we’re gonna find the answer by taking away to make 10 and then from 10.

Daniel started with 16. He took away six to make 10, then took away two more. Pick a calculation that is the same as what Daniel did. 16 take away six, 16 take away eight, or 16 take away four.

In this problem, we can see that Daniel is subtracting from a teen number. We know this for a number of reasons. We’re told that he starts with the number 16. We can see in the picture that there are 16 counters before some get crossed off. And all of our possible answers start with the number 16 too. So, we know that Daniel is trying to find the answer to 16 take away something. But what number is he trying to take away?

Well, if we read the question carefully and look at the pictures, we can see that Daniel finds the answer in two steps. First, we’re told he took away six. Now, why might Daniel split up his subtraction into two steps and only take away six to start with? Well, we’re told this again in the question. He took away six to make 10. We know this is a quick calculation to work out. 16 take away six leaves us with 10.

And you know by making 10 like this, what Daniel’s done is he’s made the calculation a lot easier cause now all he has to do is take away whatever’s left from 10. And we can subtract from 10 really quickly. We’re told that Daniel took away two more. And if we look in the bottom picture, we can see the two extra counters that Daniel’s taken away. It’s a quick way of finding the answer because Daniel probably knows that two and eight go together to make 10. So, if he subtracts two from 10, he’s going to be left with eight.

By reading the problem carefully and looking at the pictures, we can see exactly what Daniel is doing. First, he took away six, and then he took away two more. Daniel found the answer to 16 take away six take away two. And the calculation that’s the same as this is 16 take away eight.

Sophia is subtracting by making 10. 13 subtract five equals what? Which calculation should she do first? 13 take away two equals 11 or 13 take away three equals 10. And then, which calculation should she do next? 10 take away two equals eight or 10 plus two equals eight.

And maybe you’ve noticed one of these calculations doesn’t make sense, but let’s go through the question from the start and find out what Sophia is doing here. We’re told that she’s subtracting by making 10. And we can see from the picture the two numbers that Sophia’s subtracting. She’s trying to find the answer to 13 take away five.

Now, she could find the answer just by starting with the number 13 and counting back five. But we’re told that she wants to find the answer by making 10. First, she can take away part of the number five to get to 10. And then, she can take away the rest of the number five from 10 because subtracting to and from 10 is quite quick to do.

Here are 13 counters. And we can see from the diagram that Sophia has split up the five that she wants to take away into two jumps. First, she takes away three. As we’ve said already, we know why she does this; she wants to make 10. She knows that 13 take away three equals 10. So, we know the calculation that she needs to do first is 13 subtract three equals 10.

Now, Sofia knows that three and two go together to make five. She’s already taken away three out of five. Now, she needs to just subtract the remaining two. And because she’s made 10, she takes away two from 10, which is very quick to do. Now, if we look carefully to our possible answers, only one of them makes sense. 10 plus two doesn’t make eight.

But let’s think about how Sophia knows that 10 take away two equals eight. Well, she knows that two and eight go together to make 10. She can subtract from 10 really quickly. And so, the second calculation she needs to do is 10 subtract two equals eight.

Sophia found the answer to 13 subtract five by splitting up five into three and then two. The calculation she should do first is 13 take away three equals 10. And her next calculation should be 10 take away two equals eight.

Now, what’ve we learned in this video? We know that subtracting a one-digit number from a teen number can cross over the number 10. And we’ve learnt a way to find the answer in two steps. We’ve learnt how to subtract a one-digit number from a teen number by first taking away to make 10 and then taking away whatever is left from 10.

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