Subtracting Ones from Teen Numbers:
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
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
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
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
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
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.