Video Transcript
Converting Lengths: Meters and
Centimeters
In this video, we’re going to learn
how to measure length using mixed units, to convert between lengths using
partitioning, and also to compare lengths given in meters and centimeters. Which of these two snakes is
longer, the one that measures 100 centimeters or the one that measures one
meter? Well, this is a trick question to
test whether you’re awake. They’re both the same length. One meter is exactly the same
length as 100 centimeters, and it’s important that we remember this fact because
we’re going to be using it again and again in this video.
This is because we’re going to be
learning how to convert measurements so we can write them in three different ways:
in centimeters and then, depending on the measurement, either meters or meters and
centimeters. We’ll see when we need to use this
in a moment. But for now, because we know that
one meter is the same as 100 centimeters, we can start to use this to help us
convert between the two. This snake is two meters long. How many centimeters long is
it? We know that one meter is worth 100
centimeters, and so two meters would be two lots of 100 centimeters or 200
centimeters. It’s quite easy to convert between
the two when we’re thinking of whole numbers of meters.
Three meters is 300
centimeters. Four meters is 400 centimeters and
so on. And we can even work the other way,
changing centimeters into meters. This snake is 600 centimeters
long. And what’s the fact that we need to
use to help us here? We know 100 centimeters are the
same as one meter. So we need to ask ourselves, how
many lots of 100 are there in 600? There are six lots of 100 in
600. And if each of these is worth one
meter, then we know the snake is six meters long. 600 centimeters equals six
meters. They’re just different ways of
saying the same length.
So far, we’ve been looking at
measurements that are whole numbers of meters. But what about this snake? It’s 228 centimeters long. Because 228 isn’t a multiple of
100, we’re going to need to give the measurement in meters and some centimeters. And to do this, we need to start
with 228 and partition it so we take the 100s out. There are two 100s in 228, so we
can partition this number into 200 and then the 28 that’s left over. Now because we’ve split up this
number or partitioned it so that we could see the 100s, we can convert them. We know that 200 centimeters are
exactly the same as two meters, so at least we’ve changed part of our measurement
into meters. We can’t change it all though;
we’ve still got those 28 centimeters left over. This snake’s length is two meters
and 28 centimeters.
You know, we can also convert in
the opposite direction. We can start with a measurement in
meters and centimeters and then convert it so that we write it just in
centimeters. This snake is one meter and 15
centimeters long. Now we can partition this length
into a part worth one meter and another part worth 15 centimeters. A part of the length is already in
centimeters, so we don’t need to worry about this for now. Let’s just concentrate on the part
that isn’t in centimeters. How many centimeters are the same
as one meter? 100 centimeters. And we know if we put our two parts
back together again — 100 plus another 15 is 115 centimeters. One meter 15 centimeters is the
same as 115 centimeters.
Let’s have a go at answering some
questions now where we have to convert between meters and centimeters.
Look at the ruler. One meter equals 100
centimeters. How many centimeters are in three
meters? Three meters equals what
centimeters.
To begin within this question,
we’re told to look at the picture of the ruler. So, we better start by doing
that. What can we see? Looks a little bit like a number
line, doesn’t it? It starts at zero. And we can see each multiple of 10
is labeled: 10, 20, 30, and so on all the way up to 100. Now if we look at the start of the
ruler, we can see the letters cm. This shows us the unit of
measurement that our ruler shows. cm stands for centimeters. And so when we’re counting 10, 20,
30, and so on, we’re counting in centimeters. This ruler goes from zero to 100
centimeters.
But there’s something else
interesting about our ruler. Can you spot it? At the other end of the ruler,
there’s an arrow labeled one m. So if we count all the way up to
100 centimeters, it’s the same as one m. Do you know what one m stands
for? Of course, we’re told in the fact
above the ruler, aren’t we? One meter. One meter is the same as 100
centimeters, and our ruler helps to show this. Now, if one meter is the same as
100 centimeters, we can use this to help answer our question “How many centimeters
are in three meters?” Let’s use a bar model to help
us.
If we know one meter is the same as
100 centimeters, then two meters must be the same as two lots of 100 centimeters or
200 centimeters. And so to answer our question,
three meters will be the same as three lots of 100 centimeters or 300
centimeters. The number of centimeters that are
in three meters is 300. Three meters equals 300
centimeters.
Write in centimeters: eight meters
and five centimeters.
In this question, we’re given a
measurement. Now we might think at first glance
that this looks like two measurements because not only can we see a number of
meters, but also some centimeters too. But this is one single
measurement. It just means slightly more than
eight meters, eight meters and five centimeters. Now at the moment, this measurement
has been written, as we’ve said already, in meters and also centimeters. But we can convert this measurement
so that we write it just in centimeters, which is exactly what this question asks us
to do. To help us, we can split up or
partition eight meters five centimeters. And we can split it into eight
meters and five centimeters.
Now our question asks us to write
the whole measurement in centimeters. And at the moment, part of it
already is in centimeters, so we can ignore this for a moment. Let’s concentrate on the part that
isn’t in centimeters. How can we convert eight meters
into centimeters? Is there a fact we can use to help
us? We know that one meter is the same
as 100 centimeters, and so eight meters must be the same as eight lots of 100
centimeters or 800 centimeters. Now that we’ve converted our number
of meters into centimeters, both parts are written in centimeters. So we just need to add the two
parts back together again. 800 centimeters plus another five
centimeters equals 805 centimeters. We can write eight meters and five
centimeters in centimeters as 805 centimeters.
Complete: What centimeters equals
four meters and 70 centimeters.
To help us answer this question,
we’re shown a part–whole model. Now, normally, if we wanted to find
the missing number here, that’s the missing whole, with a part–whole model, we just
add the two parts together. But in this particular question, we
can’t just add four and 70 to find the answer. Can you see why? In this question, the numbers four
and 70 represent two measurements: four meters and 70 centimeters. We can’t just add four and 70
together because they’re different units. If we look at the missing number in
our part–whole model, we can see that we’re looking for a number of centimeters. And we can see this in the
question, too.
For us to write this whole
measurement in centimeters, we’re going to need to change those four meters into
centimeters, aren’t we? Is there a fact We know that can
help us? We know that one meter is the same
as 100 centimeters, and so four meters is the same as four lots of 100 centimeters
or 400 centimeters. Should we write this on our
part–whole model to help us? Instead of four meters, let’s write
400 centimeters instead. They’re exactly the same. Now we can add our two parts
together. 400 plus another 70 equals 470. And so we know that four meters and
70 centimeters is exactly the same distance as 470 centimeters. Our missing number is 470.
A red car is 411 centimeters long,
a blue car is 500 centimeters long, and a black car is three meters long. Which car is the longest?
In this question, we need to
compare the lengths of three cars. Let’s have a look at the
measurements: 411 centimeters, 500 centimeters, three meters. What do you notice about these
measurements? They’re not all measured in the
same unit, are they? We’ve got two measurements in
centimeters and one in meters. This means that we can’t just
compare the numbers and look at them and see which one is largest.
Instead, we’re going to have to
convert the measurements so that they’re all in the same unit of measurement. Should we change them all into
meters or centimeters? It doesn’t matter which we choose,
but with questions like this, we need to use a bit of common sense. Two of our measurements are already
in centimeters, so the quickest thing to do would be to change the one that’s in
meters into centimeters, and then they’re all in centimeters. We know that one meter is the same
as 100 centimeters, and so three meters is the same as three lots of 100 centimeters
or 300 centimeters.
Now that all our measurements are
in centimeters, we could show them all on a number line. A red car is 411 centimeters. That’s about here on the number
line. A blue car is 500 centimeters
long. And although we said a black car
was three meters, we worked out this was exactly the same as 300 centimeters. We made sure all our measurements
were in the same unit so that we could then compare them. The longest of the three cars is
the blue car.
So what have we learned in this
video? We’ve learned how to measure length
using mixed units, convert between lengths using partitioning, and compare lengths
given in meters and centimeters.
