# 2.Topic 3-Video 5

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In this video, we're going to learn what it means to divide whole numbers
by unit fractions.
Let's review what we already know about division.
We know that when we divide whole numbers,
we're taking a whole number
and breaking it into equal size groups.
There are 6 apples.
And, each person gets 2 apples.
We can figure out how many people will get apples,
by using the division equation,
6 divided by 2.
To solve this division problem,
we first need to ask ourselves,
how many groups of 2
are in 6 wholes.
That means we need to take our 6 apples,
and we need to put them into groups of 2.
Now, we can count
how many groups of 2 we have.
You see we have 1 group of 2,
2 groups of 2,
and 3 groups of 2.
That tells us we have 3 groups of 2
in 6 wholes.
And, 3 people can get apples.
The 6, our total number of apples, is called the dividend.
The 2,
the number of apples in each group,
in this case is called the divisor.
3, our answer, is called the quotient,
and, it tells us,
how many groups of 2 are in the 6.
Let's look at this problem, in a different way.
Let's say, we still have 6 apples.
But, each person is going to get half of an apple, this time.
We want to know
how many people are there who will get apples.
Well, now our division equation looks a little different.
We have 6 divided by half.
Instead of dividing 6 by a whole number,
we are now dividing 6 by a fraction.
One half is a unit fraction,
because, the numerator is a 1.
Any fraction with a numerator of 1,
is called a unit fraction.
In order to solve 6 divided by half,
we need to ask ourselves,
how many halves are in 6 wholes.
In order to do that,
we need to take our 6 whole apples,
and we need to divide them
into halves.
Once I've done that,
I can count how many halves
I have in the 6 whole apples.
Now, I'm going to count each half separately,
because, each half is a group in this case.
And, now I see that
there are 12 groups of halves
in 6 wholes.
I want to make sure I write the answer
to my problem,
6 divided by half,
equals 12,
and there's my problem was asking me
how many people there were
to get apples.
I am going to label that,
12 people.
Now, some of you, great mathematicians, may be noticing that
your quotient,
your answer
is actually larger
than the numbers you divided.
You're absolutely right.
That's because we divided a whole number
by a fraction.
Let's look at another problem.
Let's say there are 3 cakes.
And, each person is going to get one fourth serving of a cake.
We want to know how many people will get cake.
We can use the division equation
3 divided by one fourth
to represent this problem.
To solve this problem,
we need to ask ourselves
how many one fourth groups are in 3 wholes.
To do that
we need to slice
each whole cake
into fourths.
Now, we can count
how many groups of one fourth
are there in these 3 wholes.
I see that there are 1, 2, 3, 4,
groups of one fourth
in this 1 whole,
which means there are 4 groups of one fourth
in the others.
Now, all I have to do is count by
4s,
to make my counting quicker.
So, I have
4...
4,
8,
12.
I have 12 groups of one fourth
which means 12 people can get cake.
We can also use fraction bars
to model this problem.
The blue bars here represent our 3 wholes.
The yellow bars represent
how many groups of one fourth we have in those 3 wholes.
Again,
we see that in each whole
there are
4 groups of one fourth.
So, we have a total of
12 groups of one fourth.
Let's look at one last problem.
Say, I have 2 whole candy bars.
And, I want to share those candy bars with some friends.
So, I'm going to split or divide those candy bars into thirds.
I have the problem, 2 divided by one third
which means I nee to figure out
how many groups of one third
are in 2 wholes.
All I need to do is count
how many one thirds I see.
And, I've seen 1,
2,
3,
4,
5,
and, 6 groups
of one third
in the 2 wholes.
Now, you've learnt what it means
to divide a whole number by a unit fraction.
You're now going to try some problems
on your own.