Video Transcript
Unit Fractions
In this video, we’re going to learn
how to model and write what we call unit fractions. We’re also going to learn how to
describe the numbers in a fraction with the words numerator and denominator.
This is an unusual looking plant,
isn’t it? On each of the flower heads, the
petals are all the same color apart from one. Can you spot the one white petal on
each flower head? Let’s look at them one at a
time. This flower head has three petals,
and they’re all equally sized. But only one single petal is
white. The rest are pink. I wonder, have you ever seen a
flower like this, where one out of three petals is a completely different color?
This flower head here is split up
or divided into four equal-size petals. Again, only one petal is white, but
this time, one out of four petals is white. What fact could be right for this
flower head. There are one, two, three, four,
five parts or petals that our flower head has been split into. And they’re all the same size. And how many of these five petals
are white? It’s just one again, isn’t it? In fact, it’s only one petal every
time. This time, we can say one out of
five petals is white. And on this flower head, we can say
one out of seven petals is white.
When we write one out of something,
like we’ve done here again and again, we’re describing a number that’s part of a
whole. The part is the number one. In this example, it’s the number of
petals that are white, and it’s always one. And this number here is the
whole. This is the number of parts that
the whole amount’s been split into. In this example, it’s the number of
petals altogether.
Now, there are lots of words on
this screen, aren’t there? Wouldn’t it be good if there was a
way to write a number that was part of a whole that didn’t involve writing the words
“out of” all the time? Well, there is. And we call these types of numbers
fractions. A fraction is a special type of
number that describes part of a whole. It’s made up of two numbers with a
line in between. Let’s draw our line to begin
with.
Let’s come back to our
strange-looking flowers. Here’s where we write the top
number in a fraction. Do you want to learn the maths word
for the top number in a fraction? It’s what we call the
numerator. And what does the top number or the
numerator in a fraction tell us? It tells us the number of parts
that are being counted or the number of parts that we’re talking about. Now, if we want to write a fraction
that shows the part of this flower head that is white, we need to ask ourselves, how
many parts are we talking about when we say the white part? Well, it’s only one petal, isn’t
it? The top number or the numerator in
this fraction is going to be one because we’re just counting the petals that are
white. And there’s only one of them.
The bottom number in a fraction
goes here. Now, we’ve learned the maths word
for the top number, so we might as well learn the maths word for the bottom
number. The bottom number in a fraction is
called the denominator. Now, the denominator shows us the
number of equal parts that the whole amount has been split into. Let’s come back to our flower
head. How many equally sized petals has
the flower head been split into? One, two, three. And so, the denominator in our
fraction is three.
This fraction shows that one out of
a possible three petals are white, one out of three. And when we read this fraction, we
don’t say one out of three. We say one-third. One-third is one part out of a
total of three equal parts.
What fraction of this square have
we shaded in pink? Remember, our numerator shows us
the number of parts that we’re talking about. In this case, it’s the number of
parts that are shaded pink. And we can see that this is only
one part. But one out of how many? Our denominator’s going to show us
this. We can see that the whole amount
has been split into one, two, three, four equal parts. So, our denominator is going to be
four. The fraction of the square that’s
shaded pink is one out of four. Do you know how we say this
fraction? We can say one-quarter of the
square is pink. Another way of saying the same
thing is one-fourth of the square is pink.
By the way, did you notice when we
looked at our flowers that we were only talking about one part every time? Only one of the petals every time
was white, wasn’t it? So, even though the denominator,
which shows the number of parts altogether, was different every time, the number of
parts that we’re looking at each time is always one. The numerator in these fractions is
one. Do you remember the title of this
video, unit fractions? Well, a unit fraction is just a
fraction that has one in its numerator. In other words, in the whole of
this video, we’re only going to be thinking about one part out of a whole every
time.
One-third, one-quarter or
one-fourth, one-fifth, one-sixth, one-seventh. Perhaps in later videos, we’ll look
at some fractions where we look at more parts. But for now, let’s try answering
some questions where we have to think about unit fractions.
What fraction is shaded?
In the picture, we can see a circle
that’s been split up or divided into equal parts. Can you see that they’re all
equal? Turn your head and have a good look
at them. They’re all the same size, aren’t
they? And part of the circle has been
shaded blue. We’re asked, what fraction is
shaded? A fraction is a number that shows
part of a whole amount. And part of the circle has been
shaded, hasn’t it? So, a fraction’s a good number to
use.
When we write a fraction using
numbers, we write one number then a line and then another number underneath. The top number in a fraction is the
numerator. This is the number of parts that
are being counted, the number of parts that we’re talking about. In this question, we’re looking for
the fraction that is shaded. So, how many parts are shaded? Well, there’s only this part here,
isn’t there? The numerator or the top number in
our fraction is going to be one. Because we’re only talking about
one part, we call this a unit fraction.
The bottom number or the
denominator in a fraction is the number of equal parts that there are in the whole
amounts. How many parts has this circle been
split into? One, two, three, four, five. We call these fifths. Our denominator then is the number
five. One out of five equal parts is
shaded. And how do we say this
fraction? We can say one-fifth of the circle
is shaded. One out of five is the same as
one-fifth.
What fraction is shaded?
In the picture, we can see a
rectangle that’s been split up into lots of equal parts. How many equal parts are there? One, two, three, four, five, six,
seven, eight, nine equal parts. Can you see they’re all the same
size? Now, how many of these equal parts
are shaded? Well, there’s only this one here,
isn’t there? We could say one out of nine equal
parts is shaded. But our question asks us for a
fraction. What fraction is shaded? How can we write one out of nine
equal parts as a fraction?
Well, we know that a fraction is a
type of number that has a line, a number above it, and another number below it. The top number or the numerator in
a fraction shows us the number of parts that we’re talking about. And in this case, we’re talking
about the number of parts that are shaded. How many parts are shaded? Only one. So, our fraction has a numerator of
one.
The bottom number or the
denominator in a fraction shows us the number of equal parts that the whole amount
has been split into. And we said this rectangle has been
split into nine equal parts, didn’t we? So, our denominator is nine. One out of nine equal parts is
shaded, and so we write the fraction using numbers like this. One-ninth of the rectangle is
shaded.
Madison is going to share this
chocolate bar with her seven friends. There are what squares in
total. Each person will get what square or
squares of chocolate. Find the denominator. Each person will get one what of
the chocolate bar.
We’re shown a picture of a
chocolate bar. And we’re told that Madison is
going to share this bar with her friends. Now, we’re told the number of
friends that she’s going to share it with is seven. So, if we include Madison, because
she’s sharing it, that’s eight people together, isn’t it? Now, this question is all about
fractions. And fractions are special numbers
that help us to show part of a whole. And as Madison is going to be
splitting up this chocolate bar into different parts, a fraction is a good way to
describe it, isn’t it?
Now, to help us think about what
fractions we can see, we’ve got some sentences to complete. And the first one is about the
number of squares that there are in the chocolate bar altogether. There are what squares in
total. Let’s count them. One, two, three, four, five, six,
seven, eight. There are eight squares in
total. This is quite useful, isn’t it? Remember how many people that
Madison wanted to share her chocolate bar between. It was eight, wasn’t it? So, she has eight squares, and she
wants to share them between eight people.
Onto our second sentence. Each person will get what square or
squares of chocolate. Well, we know if there are eight
squares and Madison wants to share them between eight people, everyone’s going to
get one square each. Each person will get one square of
chocolate.
Now, we can use the information
that we’ve been given to work out what fraction of the chocolate bar each person
gets. Each person will get one what of
the chocolate bar. This number here is our
fraction. There are two numbers, and there’s
a line in between. The top number or the numerator in
a fraction tells us the number of parts that we’re talking about. And we know that each person is
going to get one part of the chocolate bar or one square. That’s where this number one comes
from on the top.
But the denominator or the bottom
number in this fraction is missing. The denominator shows us the number
of equal parts that the whole amount has been split into. In other words, each person will
get one out of how many? Can you see the sentence that’s
gonna help us with this? We found the denominator when we
added up the number of squares there were in total. There were eight, weren’t
there? Each person will get one out of
eight squares. And we read this fraction as
one-eighth.
If Madison is going to share this
chocolate bar with her seven friends, we worked out that was eight people
altogether. There are eight squares in
total. And because there are eight people,
we know each person will get one square of chocolate. And so, we can say each person will
get one-eighth of the chocolate bar.
What have we learned in this
video? We’ve learned how to model and
write unit fractions. We’ve also learned how to describe
the numbers in a fraction using the words numerator and denominator.
