Main content

## Unit conversion

Current time:0:00Total duration:5:23

# Adding units of volume

CCSS Math: 5.MD.A.1

## Video transcript

16 fluid ounces plus 3 pints
plus 4 quarts is equal to how many gallons? Now the one unfamiliar thing
here that we haven't seen before is this 16
fluid ounces. We've seen ounces before,
but not fluid ounces. And to make things confusing,
they're actually very different things. Fluid ounces are a measure
of a volume. Fluid ounces measure volume,
just like cups and pints and quarts and gallons do. While ounces measure weight. And this might make it
kind of confusing, or maybe less confusing. But it also happens that a
fluid ounce of water, at standard temperature and
pressure, is going to weigh a little bit more than
an actual ounce. So that's why they're
kind of close. A fluid ounce of water is not
that different in weight than an ounce, but they're two fundamentally different things. This is volume. This is weight. Now a fluid ounce, there's
many ways you could think of this. One is that you have 8-- let me
write it here-- you have 8 fluid ounces per cup. Or, since there are 2 cups per
pint, you also have 16 fluid ounces per pint. You could view it either way. Or you could say that you have
32 fluid ounces per quart. Or you can multiply that times
4, and that's how many fluid ounces you have per gallon. Ounces, which is a unit
of weight, you have 16 ounces per pound. And since I told you that a
fluid ounce is a little bit more that an ounce, you can kind
of figure out that, hey, a pint of water, at standard
temperature and pressure and all of that, will weigh
a little bit more. Almost a pound, or actually a
little bit more than a pound, but roughly equal to a pound. So that's something that
might make things simpler, or more difficult. Now let's actually tackle
the problem. So we have 16 fluid ounces. I just told you that there are
16 fluid ounces per pint. So 16 fluid ounces, let
me write over here. So 16 fluid ounces times-- now
we want the fluid ounces to cancel out, so we want fluid
ounces in the denominator times fluid ounces. Now how many fluid ounces
are there per pint? We want a pint in the numerator
so that this and this cancel out. We just saw it, there are 16
fluid ounces per pint, or that 1/16 of a pint per
fluid ounce. Either way. But we see this and this
will cancel out. And so 16 over 16, because 16
times 1, divided by 16, 1 equal to 1 pint. And we know that. 16 fluid ounces equal a pint. If we have 16 fluid ounces right
over here, this is 1 pint right over there. So we have 1 pint plus another
3 pints, so if we were to add all of this part right here
together, 1 pint plus 3 pints is 4 pints. Now we have 4 pints, let's
convert to quarts. Now we know that there are
2 pints per quart. Or we can view it this way, we
want the pints to cancel out, or 1 quart is 2 pints, or
1/2 quart per pint. And we wrote it this way instead
of 2 over 1 because we wanted the quarts in the
numerator, and the pints in the denominator, so that that,
and that, cancel out. And it makes sense. If you're converting a smaller
unit to a larger unit you're going to have fewer of them. So you're essentially
dividing by 2. So 4 times 1/2, or 4 divided
by 2, is equal to 2 quarts. So this whole piece right here,
these 4 pints, are equal to 2 quarts. That's 2 quarts. And you could visualize it. 2 of these combined make 1
quart, so 4 of them is going to be 2 quarts. So you have 2 quarts here,
plus another 4 quarts. So this entire quantity of 2
quarts plus this 4 quarts are going to be 6 quarts. So the entire quantity
is 6 quarts. And we have to convert
that to gallons. So let me write it right here. We have 6 quarts and we want
to convert to gallons. So we want gallons and the
numerator, and we want quarts in the denominator, so that it
cancels out with this quarts when we multiply them. And how many quarts are
there in a gallon? Or 1 gallon is 4 quarts. Or 1/4 of a gallon per quart. Now we can multiply. The quarts cancel out. You have 6 times 1/4, which
is 6/4 gallons. And now we can simplify this. We can divide the numerator
and the denominator by 2. This is the same thing
as 3/2 gallons. So 3/2 would be an acceptable
answer right here. This would be 3/2 gallons. If you want to write it as a
mixed number, 3 divided by 2 is 1 with the remainder 1. So it's 1 and 1/2 gallons. Either one would be an
acceptable answer.