How Do You Calculate Capacitance with Two Different Dielectrics?

[Brewer]

Silly question, but I can't find the answer anywhere in my notes.

When you have a capacitor with two parallel slabs of dialectric (equal thickness, different dialectric constants) in between the plates of a capacitor, would you find the capacitance by linear superposition (I wouldn't have thought so), or by an average dialectric constant?

As I say it seems a little trivial, but I can't find the answer in either my notes or my textbook!

Thanks guys

 

[gulsen]

consider then as two capacitors in series, both having half thickness, with different dielectric constants.