-
-
Let's think a little
bit about what
-
it means to multiply fractions.
-
Say I want to multiply
1/2 times 1/4.
-
Well, one way to
think about this
-
is we could view
this as 1/2 of a 1/4.
-
And what do I mean there?
-
Well let me take a whole,
let me take a whole here,
-
and let me divide
it into fourths.
-
So let me divide
it into fourths,
-
so I'll divided into
4 equal sections.
-
And so 1/4 would be 1 of
these 4 equal sections.
-
But we want to take 1/2 of that.
-
So how do we take half of that?
-
Well, we could divide this
into 2 equal sections,
-
and then just take 1 of them.
-
So divide it into
2 equal sections,
-
and then take 1 of them.
-
So we're taking this pink area,
this whole pink area is 1/4,
-
and now we're going
to take 1/2 of it.
-
We're now going
to take 1/2 of it.
-
So that's this yellow
square right over here.
-
But what fraction of the whole
does this yellow represent?
-
Well, it now represents 1
out of 1, 2, 3, 4, 5, 6, 7,
-
8 equal sections.
-
So this right over here, this
represents 1/8 of the whole.
-
And so we see conceptually
that 1/2 times 1/4,
-
it completely makes sense,
that 1/2 of 1/4 should be 1/8.
-
And it hopefully makes
sense that you get this 8
-
by multiplying
the 2 times the 4.
-
You started with
4 equal sections,
-
but then you divided each
of those 4 equal sections
-
into 2 equal sections.
-
So then you have 8
total equal sections
-
that you split your whole into.
-
Let's do another
example, but now let's
-
multiply two
fractions that don't
-
have 1's in the numerator.
-
So let's multiply, let's
multiply 2/3 times 4/5.
-
And I encourage you
now to pause the video
-
and do something very
similar to what I just did.
-
Try to represent 4/5
of a whole and then try
-
to represent 2/3 of that
4/5 and see what fraction
-
of the whole you actually have.
-
So pause now.
-
So let's think about this.
-
Let's represent 4/5.
-
So if I have a
whole like this, let
-
me try to divide it
into 5 equal sections.
-
5 equal sections, so let's say
that is 1 equal section, that
-
is 2 equal sections, that is
3, 4, and 5-- I can do a better
-
job than this.
-
This is always the hard part.
-
I'm trying my best to
make them look, at least,
-
like equal sections--
2, 3, 4, and 5.
-
I think you get the point here.
-
I'm trying to make
them equal sections.
-
And we want 4/5.
-
So we want 4 of these
5 equal sections.
-
So this would be 1 of the 5
equal sections, 2 of them,
-
3 of them, and then 4 of them.
-
So that right over there is 4/5.
-
Now we can view this
as 2/3 of the 4/5.
-
So how can we think about that?
-
Well, we could take this section
and divide it into thirds.
-
So let's do that.
-
Divide it into thirds.
-
So we're going divide it
into 3 equal sections.
-
So that's 1/3, and then 2/3.
-
So we took each of
the 5 equal sections,
-
and we divided them
into 3 equal sections.
-
Now what's going to
be 2/3 of the 4/5?
-
Well, that's going to be
this part right over here.
-
So let me make this clear.
-
This is 1/3 of the 4/5.
-
And then this would
be 2/3 of the 4/5.
-
So this right over here, would
be 2/3 of the 4/5, or 2/3 times
-
4/5.
-
But what fraction of the
whole does that represent?
-
Well, how many total, how many
total equal sections do we now
-
have?
-
Well, we have 1, 2, 3, 4, 5,
6, 7, 8, 9, 10, 11, 12, 13, 14,
-
15.
-
So we have 15 equal sections.
-
I'm using a new color.
-
We have 15 equal sections,
and that make sense.
-
We started with
5 equal sections,
-
but then we divided each of
those into 3 equal sections.
-
So now we have 5 times
3 total equal sections.
-
And then how many of
those are now colored in?
-
Well, we see it's 2 times 4.
-
1, 2, 3, 4, 5, 6, 7, 8.
-
How many of them are in the
2/3 of the 4/5, I should say.
-
And there's 8 of them, 8
of the 15 equals sections.
-
And so there you have it.
-
It should hopefully
now make visual sense,
-
or it makes conceptual
sense, that 2/3 times 4/5--
-
you can obviously compute
it by just multiplying
-
the numerators, 2 times 4 is 8.
-
And then multiplying the
denominators, 3 times 5 is 15--
-
but hopefully this now makes
conceptual sense as 2/3 of 4/5.
-