Using volume of a sphere, calculate the average density of Saturn (radius = 60,268 km).
The volume is, of course,
V (4/3)pi*R^3.
You will have to look up Saturn's mass, M. It is easily Googled.
The average density is M/V
You should find that it is about 2/3 of the density of water.
For additional help,
http://www.universetoday.com/15322/density-of-saturn/