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
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.