Ohms - power rating conversion?

Just looking for some help here,
I'm trying to figure out the 8ohm power rating for power amplifier that only gives spec's for 4 and 2ohm power ratings.

What I'm looking at gives 1250w@4ohms and 1500w@2ohms, however I'm running an 8ohm PA system.

How do you convert the 4ohm power rating into 8ohms? And what would it be in this situation?
Also since a rating for 8ohms isn't given does this mean the amplifier isn't capable of holding an 8ohm load (even though it is less demanding load compared to 4 and 2ohms)?

Note: The PA system won't be running in series, this is direct one output to one input.

well personally i havent a clue how to do it,but if you can figure this out your set.

http://www.onlineconversion.com/ohms_law.htm

\M/(*-+)
gs2112

Well watts are power and ohms are resistance

V=I/R and P=IV

Therefore the watts it will give would be equivilant to P=RV^2 or power=resistance multipled by voltage squared.

Although personally I'd treat anything you work out this with caution. Not because the equation is wrong but because I'm not 100% sure if this is the right context (AC vsDC power etc)

Cheers for the response guys, I managed to see my uni lecturer about it and from my understanding i goes like this:

all ratios referenced the power rating @4ohms.
8ohms = 100w = .5
4ohms = 200w = 1
2ohms = 400w = 2