Current time:0:00Total duration:17:02

# Intro to division

## Video transcript

I think you've probably heard
the word divide before, where someone tells you to
divide something up. Divide the money between you
and your brother or between you and your buddy. And it essentially means
to cut up something. So let me write down
the word divide. Let's say that I
have 4 quarters. Do my best to draw
the quarters. If I have 4 quarters
just like that. That's my rendition of George
Washington on the quarters. And let's say there's two of
us and we're going to divide the quarters between us. So this is me right here. Let me try my best to draw me. So that's me right there. Let's see, I have
a lot of hair. And then this is
you right there. Do my best. So you're bald. You have side burns. Maybe you have a little
bit of a beard. I want to get too
focused on the drawing. So that's you, that's me, and
we're going to divide these 4 quarters between the 2 of us. So notice, we have 4 quarters
and we're going to divide between the 2 of us. There are 2 of us. And I want to stress
the number 2. So we're going to divide
4 quarters by 2. We're going to divide it
between the 2 of us. And you've probably done
something like this. What happens? Well, each of us are
going to get 2 quarters. So let me divide it. We're going to
divide it into 2. Essentially what I did do is
I take the 4 quarters and I divide it into 2 equal groups. And that's what division is. We cut up this group of
quarters into 2 equal groups. So when you divide 4 quarters
into 2 groups, so this was 4 quarters right there. And you want to divide
it into 2 groups. This is group 1. Group 1 right here. And this is group 2 right here. How many numbers
are in each group? Or how many quarters
are in each group? Well, in each group I
have 1, 2 quarters. Let me use a brighter color. I have 1, 2 quarters
in each group. 1 quarter and 2 quarters
in each group. So to write this out
mathematically, I think this is something that you've done,
probably as long as you've been splitting money between you and
your siblings and your buddies. Actually, let me scroll over
a little bit, so you can see my entire picture. How do we write this
mathematically? We can write that 4
divided by-- so this 4. Let me use the right colors. So this 4, which is this 4,
divided by the 2 groups, these are the 2 groups: group 1 and
this is group 2 right here. So divided into 2 groups
or into 2 collections. 4 divided by 2 is equal to--
when you divide 4 into 2 groups, each group is going
to have 2 quarters in it. It's going to be equal to 2. And I just wanted to use this
example because I want to show you that division is something
that you've been using all along. And another important, I guess,
takeaway or thing to realize about this, is on some level
this is the opposite of multiplication. If I said that I had 2 groups
of 2 quarters I would multiply the 2 groups times the 2
quarters each and I would say I would then have 4 quarters. So on some level these are
saying the same thing. But just to make it a little
bit more concrete in our head, let's do a couple
of more examples. Let's do a bunch
of more examples. So let's write down, what is
6 divided by-- I'm trying to keep it nice and color coded. 6 divided by 3, what
is that equal to? Let's just draw 6 objects. They can be anything. Let's say I have
6 bell peppers. I won't take too much
trouble to draw them. Well, that's not what a
bell pepper looks like, but you get the idea. So 1, 2, 3, 4, 5, 6. And I'm going to
divide it by 3. And one way that we can think
about that is that means I want to divide my 6 bell peppers
into 3 equal groups of bell peppers. You could kind of think of it
if 3 people are going to share these bell peppers, how
many do each of them get? So let's divide it
into 3 groups. So that's our 6 bell peppers. I'm going to divide
it into 3 groups. So the best way to divide it
into 3 groups is I can have 1 group right there, 2 groups, or
the second group right there, and then, the third group. And then each group will have
exactly how many bell peppers? They'll have 1, 2. 1, 2. 1, 2 bell peppers. So 6 divided by 3
is equal to 2. So the best way or one way to
think about it is that you divided the 6 into 3 groups. Now you could view that a
slightly different way, although it's not completely
different, but it's a good way to think about it. You could also think of
it as 6 divided by 3. And once again, let's
say I have raspberries now-- easier to draw. 1, 2, 3, 4, 5, 6. And here, instead of
dividing it into 3 groups like we did here. This was 1 group, 2
group, 3 groups. Instead of dividing into 3
groups, what I want to do is say well, if I'm dividing
6 divided by 3, I want to divide it into groups of 3. Not into 3 groups. I want to divide it
into groups of 3. So how many groups of
3 am I going to have? Well, let me draw
some groups of 3. So that is one group of 3. And that is two groups of 3. So if I take 6 things and I
divide them into groups of 3, I will end up with 1, 2 groups. So that's another way to
think about division. And this is an
interesting thing. When you think about these two
relations, you'll see a relationship between 6 divided
by 3 and 6 divided by 3. Let me do that right here. What is 6 divided by 2 when
you think of it in this context right here? 6 divided by 2, when you
do it like that-- let me draw 1, 2, 3, 4, 5, 6. When we think about 6 divided
by 2 in terms of dividing it into 2 groups, what we can end
up is we could have 1 group like this and then 1 group
like this, and each group will have 3 elements. It'll have 3 things in it. So 6 divided by 2 is 3. Or you could think of
it the other way. You could say that 6 divided
by 2 is-- you're taking 6 objects: 1, 2, 3, 4, 5, 6. And your dividing it into
groups of 2 where each group has 2 elements. And that on some level is
an easier thing to do. If each group has 2 elements,
well, that's the 1 right there. They don't even have
to be nicely ordered. This could be one group right
there and that could be the other group right there. I don't have to draw
them all stacked up. These are just groups of 2. But how many groups do I have? I have 1, 2, 3. I have 3 groups. But notice something, it's no
coincidence that 6 divided by 3 is 2 and 6 divided by 2 is 3. Let me write that down. We get 6 divided by 3 is
equal to 2 and 6 divided by 2 is equal to 3. And the reason why you see this
relation where you can kind of swap this 2 and this 3 is
because 2 times 3 is equal to 6. Let's say I have 2 groups of 3. Let me draw 2 groups of 3. So that's 1 group of 3 and then
here's another group of 3. So 2 groups of 3 is equal to 6. 2 times 3 is equal to 6. Or you could think of
it the other way if I have 3 groups of 2. So that's 1 group
of 2 right there. I have another group
of 2 right there. And then I have a 3
group of 2 right there. What is that equal to? 3 groups of 2-- 3 times 2. That's also equal to 6. So 2 times 3 is equal to 6. 3 times 2 is equal to 6. We saw this in the
multiplication video that the order doesn't matter. But that's the reason why if
you want to divide it, if you want to go the other way-- if
you have 6 things and you want to divide it into
groups of 2, you get 3. If you have 6 and you want
to divide into groups of 3, you get 2. Let's do a couple
of more problems. I think it'll really
make sense about what division is all about. Let's do an interesting one. Let's do 9 divided by 4. So if we think about 9 divided
by 4, let me draw 9 objects. 1, 2, 3, 4, 5, 6, 7, 8, 9. Now when you divide by 4, for
this problem, I'm thinking about dividing it
into groups of 4. So if I want to divide it
into groups of 4, let me try doing that. So here is one group of 4. I just picked any of
them right like that. That's one group of 4. Then here's another
group of 4 right there. And then I have this
left over thing. Maybe we could call it a
remainder, where I can't put this one into a group of 4. When I'm dividing by 4
I can only cut up the 9 into groups of 4. So the answer here, and this is
a new concept for you maybe, 9 divided by 4 is going
to be 2 groups. I have one group here and
another group here, and then I have a remainder of 1. I have 1 left over that I
wasn't able to do with. Remainder-- that
says remainder 1. 9 divided by 4 is
2 remainder 1. If I asked you what 12 divided
by 4 is, so let me do 12. 1, 2, 3, 4, 5, 6, 7,
8, 9, 10, 11, 12. So let me write that down. 12 divided by 4. So I want to divide these
12 objects-- maybe they're apples or plums. And divide them
into groups of 4. So let me see if I can do that. So this is one group
of 4 just like that. This is another group
of 4 just like that. And this is pretty
straightforward. And then I have a third
group of 4 just like that. And there's nothing left
over like I had before. I can exactly divide 12
objects into 3 groups of 4. 1, 2, 3 groups of 4. So 12 divided by
4 is equal to 3. And we can do the exercise that
we saw on the previous video. What is 12 divided by 3? Let me do a new color. 12 divided by 3. Now based on what we've learn
so far we say, that should just be 4 because 3 times 4 is 12. But let's prove
it to ourselves. So 1, 2, 3, 4, 5, 6,
7, 8, 9, 20, 11, 12. Let's divide it
into groups of 3. And I'm going to make them a
little strange looking just so you see that you don't
always have to do it into nice, clean columns. So that's a group
of 3 right there. 12 divided by 3. Let's see, here is another
group of 3 just like that. And then, maybe I'll take
this group of 3 like that. And I'll take this group of 3. There was obviously a much
easier way of dividing it up then doing these weird l-shaped
things, but I want to show you it doesn't matter. You're just dividing
it into groups of 3. And how many groups do we have? We have one group. Then we have our second
group right here. And then we have our
third group right there. And then we have-- let me
do it in a new color. And then we have our
fourth group right there. So we have exactly 4 groups. And when I say there was an
easier way to divide it, the easier way was obviously, maybe
not obviously-- if I want to divide these into groups of 3 I
could have just done 1, 2, 3, 4 groups of 3. Either of these I'm
dividing the 12 objects into packets of 3. You can imagine them that way. Let's do another one that
maybe has a remainder. Let's see. What is 14 divided by 5? So let's draw 14 objects. 1, 2, 3, 4, 5, 6, 7, 8,
9, 10, 11, 12, 13 14. 14 objects. And I'm going to divide
it into groups of 5. Well, the easiest thing is
there's one group right there, two groups right there. But then this last one, I
only have 4 left, so I can't make another group of 5. So the answer here is I can
make 2 groups of 5 and I'm going to have a remainder--
r for remainder-- of 4. 2 remainder 4. Now, once you get enough
practice, you're not always going to be wanting to draw
these circles and dividing them up like that. Although that would
not be incorrect. So another way to think about
this type of problem is to say, well, 14 divided by 5,
how do I figure that out? Actually, another way
of writing this and no harm in showing you. I could say 14 divided by 5 is
the same thing as 15 divided by-- this sign right--
divided by 5. And what you do is you
say, well, let's see. How many times does
5 go into 14? Well, let's see. 5 times and you kind
of do multiplication tables in your head. 5 times 1 is equal to 5. 5 times 2 is equal to 10. So that's still less than 14,
so 5 goes at least two times. 5 times 3 is equal to 15. Well that's bigger than 14,
so I have to go back here. So 5 only goes two times. So it goes 2 times. 2 times 5 is 10. And then you subtract. You say 14 minus 10 is 4. And that's the same
remainder as right here. Well, I could divide 5 into
14 exactly two times, which would get us 2 groups of 5. Which is essentially just 10. And we still have
the 4 left over. Let me do a couple of more just
to really make sure you get this stuff really, really,
really, really well. Let me write it in
that notation. Let's say I do 8 divided by 2. And I could also write
this as 8-- so I want to know what that is. That's a question mark. I could also write this
as 8 divided by 2. And the way I do either of
these, I'll draw the circles in the second, but the way I do it
without drawing the circles, I say, well, 2 times
1 is equal to 2. So that definitely goes into 8,
but maybe I can think of a larger number that goes into--
that when I multiply it by 2 still goes into 8. 2 times 2 is equal to 4. That's still less than 8. So 2 times 3 is equal to 6. Still less than 8. 2 times-- oh, something
weird happened to my pen. 2 times 4 is exactly
equal to 8. So 2 goes into 8 four times. So I could say 2 goes
into 8 four times. Or 8 divided by 2
is equal to 4. We can even draw our circles. 1, 2, 3, 4, 5, 6, 7, 8. I drew them messy on purpose. Let's divide them
into groups of 2. I have one group of 2, two
groups of 2, three groups of 2, four groups of 2. So if I have 8 objects, divide
them into groups of 2, you have four groups. So 8 divided by 2 is 4. Hopefully you found
that helpful.