How do you find the resulting frequency of sampling a tone at too slow of a rate?
Your subsample frequency can be found as

fsub = fc mod fsamp

so, 300 Hz, in your case.

For a more complete solution, here's what I do in Matlab:

function Fif = SubsampleMap(f, fs)

   f_new = mod(f,fs);
   if f_new &gt; fs/2
       Fif = fs-f_new;
   else
       Fif = f_new;
   end


In other words, if the mod operation translates to the imaginary frequency, adjust it to the real one.