Quick review: This example shows you how to calculate
density. You've already done that. You divide the mass by the volume and that gives you
the density. 
Mass = 5.0 g
Volume = 2.0 mL 
What is the density? 
Density = 
5.0 g
2.0 mL 
= 2.5 g/mL 

Now that we know the density for this material, we can
calculate how much 6.0 milliliters of it would weigh as asked for here. Take the 6.0
milliliters and then use the density 2.5 grams per milliliter as a conversion factor. The
2.5 goes on top with the grams and the one milliliter goes on the bottom because you want
to cancel out milliliters and end up with grams. The result is 15 grams. 
How much would 6.0 mL weigh? 
6.0 mL x 
2.5 g
1 mL 
= 15 g 

Here we are asked how much volume would four grams of this
material occupy? You start with 4.0 grams and multiply by one milliliter over 2.5 grams
and you come up with the answer of 1.6 milliliters. 
How much volume would 4.0 g take up? 
4.0 g x 
1 mL
2.5 g 
= 1.6 mL 
