### Video Transcript

Arrange in descending order: 3.9
liters, 6600 milliliters, 6.9 liters, 2800 milliliters.

The first thing we should notice
here is that we’re given quantities that have two different units. Some are given in liters and some
are given in milliliters. Before we can put these in order,
they’ll need to be in the same unit, so we can either change them all to liters or
all to milliliters. Either way, we’ll need to remember
the important conversion that in 1000 millimeters, there’s one liter.

So let’s take our liter quantities
and change these into values in milliliters. To change a quantity in liters into
milliliters, we can multiply by 1000. So let’s take our value of 3.9
liters and multiply 3.9 by 1000. When we multiply by 1000, we move
all our digits three places to the left. So our value will be 3900
milliliters. 6600 milliliters is already in
milliliters, but we’ll bring it down so that we can compare it in a second.

6.9 is a value in liters, so once
again we’ll need to multiply it by 1000 to find the equivalent value in
milliliters. Once again, we move all of the
digits three places to the left when we’re multiplying by 1000, so this will give us
6900 milliliters. Finally, we have the value of 2800
milliliters.

Now, let’s put these four values in
order, but we must be careful. We’re told that it should be in
descending order. That’s from the largest value to
the smallest value. Looking at our four quantities
then, we could see that the largest one is 6900 milliliters. But we should be careful as we want
to give it in its original form. That’s 6.9 liters. Going down in size then, our next
quantity would be 6600 milliliters, which we can write in the same way as it was
originally given. Next, we have 3900 milliliters,
which we’ll write as 3.9 liters. And so we’re left with one value,
2800 milliliters. And we can check that it is indeed
the smallest of these values.

We can, therefore, give the answer
that these quantities in descending order are 6.9 liters, 6600 milliliters, 3.9
liters, and 2800 milliliters. In this approach, we changed all of
our values into a quantity in milliliters. We could have also changed them all
into liters. 3.9 liters and 6.9 liters would
have stayed the same. 6600 milliliters would have been
6.6 liters. And 2800 milliliters would be 2.8
liters. The largest value in liters would
still be 6.9 liters, followed by 6.6 liters — which is 6600 milliliters — followed
by 3.9 liters, and finally, our quantity of 2.8 liters, which was 2800
milliliters. And so we’ve confirmed our
answer.