WEBVTT
00:00:02.070 --> 00:00:07.630
Subtracting Ones from Teen Numbers: Subtracting from 10
00:00:08.790 --> 00:00:21.460
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.
00:00:29.280 --> 00:00:33.700
Now that we’ve got the title page out of the way, it’s time to let you into a little secret.
00:00:34.710 --> 00:00:55.840
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?
00:00:56.520 --> 00:01:02.640
In this video, all we really need to know how to do is subtract from 10.
00:01:03.240 --> 00:01:10.180
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.
00:01:10.800 --> 00:01:20.990
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.
00:01:21.770 --> 00:01:23.790
Seven and three make 10.
00:01:24.480 --> 00:01:29.740
So 10 take away three must leave us with the number that goes together with three to make 10.
00:01:30.540 --> 00:01:31.800
We’re left with seven.
00:01:32.880 --> 00:01:39.210
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.
00:01:40.120 --> 00:01:41.640
And we can see that the answer is one.
00:01:42.400 --> 00:01:51.070
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.
00:01:51.780 --> 00:01:54.630
So subtracting from 10 is really quick.
00:01:55.360 --> 00:02:00.080
And let’s see now how we can use it to help us when we have to work with teen numbers.
00:02:00.880 --> 00:02:05.940
Let’s imagine that we’ve been asked to find the answer to 16 take away seven.
00:02:06.800 --> 00:02:09.530
We could use 16 counters to help us here.
00:02:10.660 --> 00:02:14.820
16 is one of these teen numbers that we’ve been talking about.
00:02:15.510 --> 00:02:18.660
It’s made up of a 10 and some ones.
00:02:19.510 --> 00:02:23.100
In fact, let’s split it up into a 10 and some ones.
00:02:23.450 --> 00:02:26.480
We could put 10 counters in a box.
00:02:27.180 --> 00:02:32.250
This helps us to see that 16 is made up of 10 and six more.
00:02:32.980 --> 00:02:36.000
And remember, we need to take away seven from this amount.
00:02:36.340 --> 00:02:39.170
Can you see a way to take away seven really quickly?
00:02:39.550 --> 00:02:41.460
Why don’t we take it away from this 10?
00:02:41.680 --> 00:02:46.320
Because, as we’ve said already, subtracting from 10 is really quick.
00:02:46.990 --> 00:02:50.290
Can you think of the number that pairs with seven to make 10?
00:02:51.150 --> 00:02:53.610
Seven and three makes 10.
00:02:54.440 --> 00:02:59.240
And so if we take away seven from 10, we’re left with three.
00:03:00.100 --> 00:03:03.790
Now, remember, our question is all about subtracting from 16.
00:03:04.090 --> 00:03:08.550
So in order to find the answer, we’re gonna have to combine our two parts back together again.
00:03:08.930 --> 00:03:14.760
We have three counters left over here and those six ones that we separated at the start.
00:03:15.380 --> 00:03:19.380
And three plus six equals nine.
00:03:20.110 --> 00:03:25.440
And that’s how we know that 16 take away seven equals nine.
00:03:26.240 --> 00:03:30.890
And that’s why we said that in this video we’re going to be practising the skill of subtracting from 10.
00:03:31.590 --> 00:03:43.170
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.
00:03:44.060 --> 00:03:47.880
The only other thing we need to remember is to put the two parts back together at the end.
00:03:48.630 --> 00:03:53.370
Let’s try answering some questions now where we have to subtract a number of ones from a teen number.
00:03:54.030 --> 00:03:59.690
And each time we do, let’s look for the way that we can find the answer by subtracting from 10.
00:04:02.350 --> 00:04:08.060
Which addition expression is equal to 14 subtract nine?
00:04:09.140 --> 00:04:15.590
In this question, we’re given a subtraction to think about, 14 take away nine.
00:04:16.590 --> 00:04:18.880
Can you see it’s written underneath the question, too?
00:04:19.870 --> 00:04:26.440
But instead of finding the answer to 14 take away nine, this is a really interesting question.
00:04:26.780 --> 00:04:32.760
It says, “Which addition expression is the same as 14 take away nine?”
00:04:33.410 --> 00:04:41.840
In other words, what numbers can we add together that will be the same as if we had 14 and took away nine?
00:04:42.860 --> 00:04:45.950
Thankfully, we’ve got a picture of some counters here to help us.
00:04:46.640 --> 00:04:48.850
Now something’s happened to these counters.
00:04:49.730 --> 00:04:58.260
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.
00:04:59.050 --> 00:05:02.300
So to begin with, let’s take 14 counters.
00:05:02.980 --> 00:05:06.070
Now we need to take away nine counters from 14.
00:05:06.780 --> 00:05:16.860
And to help us do this quickly, we can split up the number 14 into two parts, because 14 is a teen number.
00:05:17.610 --> 00:05:21.890
We can split it up into 10 and four more.
00:05:22.980 --> 00:05:27.830
One 10 and four ones is the same as 14.
00:05:28.680 --> 00:05:31.920
Now, at the moment our four ones are in a bit of a square shape.
00:05:32.440 --> 00:05:39.530
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?
00:05:40.230 --> 00:05:43.720
Now, why would we want to split up 14 like this?
00:05:44.570 --> 00:05:47.770
Well, remember, we need to take away nine counters.
00:05:48.790 --> 00:05:56.050
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.
00:05:56.940 --> 00:06:01.430
So what our picture is showing us is that we can take away nine from 10.
00:06:02.290 --> 00:06:14.050
One, two, three, four, five, six, seven, eight, nine.
00:06:14.740 --> 00:06:17.210
We only have one counter left.
00:06:18.180 --> 00:06:20.810
Of course, you probably knew this before we started, didn’t you?
00:06:21.220 --> 00:06:25.210
We know that nine and one go together to make 10.
00:06:25.840 --> 00:06:30.770
So if we start with 10 and we take away nine, we’re going to be left with one.
00:06:32.160 --> 00:06:38.730
Now although we’ve found out what 10 take away nine is, remember, we needed to find out what 14 take away nine was.
00:06:39.250 --> 00:06:48.170
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.
00:06:49.340 --> 00:06:53.670
One plus another four equals five.
00:06:54.600 --> 00:06:59.450
And so we can say that 14 subtract nine leaves us with five.
00:07:00.350 --> 00:07:11.450
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.
00:07:12.380 --> 00:07:18.760
Well, there are lots of additions that make five, but there’s only one that we’ve used in this question.
00:07:19.750 --> 00:07:20.750
Can you spot it?
00:07:21.430 --> 00:07:28.050
It was when we added our one remaining counter back together with our four counters.
00:07:28.620 --> 00:07:32.570
It was when we said one plus four equals five.
00:07:33.410 --> 00:07:41.360
The addition expression that we found that was the same as 14 take away nine is one plus four.
00:07:45.890 --> 00:07:48.720
What is 14 subtract eight.
00:07:49.860 --> 00:07:53.260
Hint: Subtract from 10.
00:07:54.580 --> 00:07:59.620
It looks like we need to take away a ones number from a teen number in this question.
00:08:00.330 --> 00:08:03.590
We need to subtract eight from 14.
00:08:04.530 --> 00:08:05.680
But wait a second.
00:08:06.490 --> 00:08:11.580
The hint that we’re given doesn’t say subtract from 14; it says subtract from 10.
00:08:12.910 --> 00:08:13.800
Why did it say this?
00:08:13.800 --> 00:08:15.670
It’s a bit strange.
00:08:16.610 --> 00:08:21.200
In the picture, we can see 14 counters that are being put into 10 frames.
00:08:21.510 --> 00:08:24.350
And this gives us a little bit of a clue as to what we need to do.
00:08:24.830 --> 00:08:34.630
Because by using 10 frames, we can see that the number 14 is the same as one lot of 10 and then four ones.
00:08:35.680 --> 00:08:44.660
So instead of taking away eight from 14, by splitting the number up like this, we can take away eight from 10.
00:08:45.640 --> 00:08:47.790
And this is what the hint is really telling us.
00:08:48.350 --> 00:08:51.950
It’s really saying to us, don’t take away from the whole amount.
00:08:52.370 --> 00:08:57.910
Now that you’ve split up 14 into one 10 and four ones, just look at the one 10.
00:08:58.120 --> 00:09:00.460
It’s much easier to subtract from 10.
00:09:01.460 --> 00:09:09.740
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.
00:09:10.800 --> 00:09:17.890
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.
00:09:18.640 --> 00:09:25.320
Now, if we draw a line here on our 10 frame, we can see that eight and another two go together to make 10.
00:09:26.170 --> 00:09:31.690
So if we start with 10 and take away eight, we’ll be left with two.
00:09:32.760 --> 00:09:38.190
Now remember, the calculation we’re trying to work out here is 14 take away eight.
00:09:39.180 --> 00:09:44.450
So to see how many counters we’ve got left, we need to add the two parts we’ve got back together again.
00:09:45.250 --> 00:09:49.710
And two plus four equals six.
00:09:50.760 --> 00:09:58.320
To find the answer to 14 take away eight, we first split up the number 14 into 10 and four.
00:09:58.990 --> 00:10:06.040
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.
00:10:06.940 --> 00:10:09.820
10 take away eight leaves us with two.
00:10:10.570 --> 00:10:12.810
Then we had to put the two parts back together again.
00:10:13.110 --> 00:10:16.720
Two plus the four ones equals six altogether.
00:10:17.380 --> 00:10:22.370
And that’s how we know that 14 subtract eight equals six.
00:10:26.920 --> 00:10:32.490
Fill in the blank: 10 take away seven equals what.
00:10:33.960 --> 00:10:39.820
And then fill in the blank: 15 take away seven equals what.
00:10:41.180 --> 00:10:42.900
This question has two parts.
00:10:42.900 --> 00:10:43.910
And did you notice?
00:10:44.080 --> 00:10:44.950
They’re linked.
00:10:45.640 --> 00:10:48.990
In both parts, we need to take away seven.
00:10:49.780 --> 00:10:53.760
In the first part, we’re asked to start with 10 and take away seven.
00:10:54.440 --> 00:10:59.480
But then, in the second part, we need to find the answer to 15 take away seven.
00:11:00.030 --> 00:11:04.230
And why do you think we’re given two similar calculations like this one after another?
00:11:04.480 --> 00:11:09.080
Do you think maybe the first calculation might help us find the answer to the second?
00:11:09.990 --> 00:11:11.020
Let’s find out.
00:11:11.560 --> 00:11:20.360
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.
00:11:21.010 --> 00:11:25.460
We just need to remember the facts we know about the numbers that go together to make 10.
00:11:26.530 --> 00:11:30.130
Now do you remember what goes together with seven to make 10?
00:11:31.350 --> 00:11:35.850
We know that seven and three makes 10.
00:11:36.270 --> 00:11:41.640
And so if we start with 10 and take away seven, we’re going to be left with three.
00:11:42.320 --> 00:11:49.180
So if 10 take away seven equals three, how could we use this to help us find the answer to 15 take away seven.
00:11:49.980 --> 00:12:00.970
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.
00:12:01.730 --> 00:12:12.470
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.
00:12:13.360 --> 00:12:19.460
As we’ve said already, 10 take away seven is going to leave us with three.
00:12:20.430 --> 00:12:29.280
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.
00:12:29.920 --> 00:12:34.600
And we know that three plus another five equals eight altogether.
00:12:35.370 --> 00:12:39.510
And that’s how we know that 15 take away seven equals eight.
00:12:40.310 --> 00:12:46.120
We’ve used a fact to do with subtracting from 10 to help us take away from a teen number.
00:12:47.000 --> 00:12:49.820
10 take away seven equals three.
00:12:50.710 --> 00:12:54.790
And so we know that 15 take away seven equals eight.
00:12:59.740 --> 00:13:02.600
Subtract eight from 13.
00:13:03.620 --> 00:13:07.300
Hint: How can subtracting from 10 help you?
00:13:07.950 --> 00:13:10.940
13 take away eight equals what.
00:13:11.750 --> 00:13:16.510
In this question, we’re being asked to subtract or take away eight from 13.
00:13:17.020 --> 00:13:28.360
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.
00:13:29.160 --> 00:13:32.760
Well, this isn’t right at all, and we need to think carefully about what the words mean.
00:13:33.270 --> 00:13:38.700
We need to subtract or take away eight from 13.
00:13:39.170 --> 00:13:43.850
In other words, we start with 13, and we take away eight from it.
00:13:43.880 --> 00:13:51.280
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.
00:13:51.910 --> 00:13:54.750
So we need to find the answer to 13 take away eight.
00:13:54.750 --> 00:13:56.070
But we’re given a hint here.
00:13:56.610 --> 00:14:00.380
We’re asked how can subtracting from 10 help you?
00:14:01.260 --> 00:14:04.930
And underneath this question, we’re given a little clue to help us.
00:14:05.800 --> 00:14:09.170
We can see the calculation 13 take away eight.
00:14:09.670 --> 00:14:16.490
But we can also see that the number 13 has been split up into 10 and three.
00:14:17.490 --> 00:14:21.530
Now often, when we split up numbers like this, we put the larger number first.
00:14:22.090 --> 00:14:24.640
So you might be expecting it to look a little bit like this.
00:14:25.580 --> 00:14:28.720
But, you know, there’s a reason they’ve been written the other way around.
00:14:29.390 --> 00:14:32.580
And it’s all to do with how useful both parts are to us.
00:14:33.010 --> 00:14:35.830
Remember, we need to take away eight from this number.
00:14:36.640 --> 00:14:40.700
Can we take away eight from three or 10?
00:14:41.580 --> 00:14:43.850
Well, we know three is too small, isn’t it?
00:14:44.500 --> 00:14:47.890
But we can easily and quickly subtract eight from 10.
00:14:48.120 --> 00:14:51.980
All we have to do is think of the number that goes together with eight to make 10.
00:14:52.740 --> 00:15:00.600
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.
00:15:01.280 --> 00:15:08.680
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.
00:15:09.350 --> 00:15:11.870
Now what do we put together with eight to make 10?
00:15:12.820 --> 00:15:15.920
We know that eight and another two make 10.
00:15:16.860 --> 00:15:22.790
So if we take away eight from the 10 part of our number 13, we’re going to be left with two.
00:15:23.440 --> 00:15:27.150
But remember, our number 13 isn’t just made up of 10.
00:15:27.530 --> 00:15:30.170
It’s also made up of those three ones.
00:15:30.930 --> 00:15:39.330
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.
00:15:39.760 --> 00:15:45.200
And we know that two plus another three equals five altogether.
00:15:45.870 --> 00:15:51.080
And so we can say that 13 take away eight must be worth five.
00:15:52.160 --> 00:15:56.300
So in this question, we needed to find the answer to 13 subtract eight.
00:15:56.890 --> 00:15:59.110
And our hint asked us another question.
00:15:59.310 --> 00:16:01.810
How can subtracting from 10 help you?
00:16:02.520 --> 00:16:09.300
Well, how it can help us is that we can split up the number 13 into 10 and three.
00:16:09.710 --> 00:16:20.610
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.
00:16:21.300 --> 00:16:23.790
We know that 10 take away eight is two.
00:16:25.080 --> 00:16:29.350
And so 13 take away eight is just going to be three more than this.
00:16:30.050 --> 00:16:33.530
13 take away eight equals five.
00:16:35.820 --> 00:16:37.340
What have we learned in this video?
00:16:38.530 --> 00:16:47.750
We’ve learned how to subtract a one-digit number from a teen number by subtracting from 10 to help.