I don't know the exact numbers, but I'm > 2200 through Rx at the moment, and my score report says I've completed 213, 224, 96 and 39 questions for biochemistry, microbiology, behavioral science and epidemiology, respectively.
So multiplying by 3/2.2 (since there are ~3000 Q's total) = what should be roughly > 290, 305, 131 and 53 questions, respectively, for those subject areas.
On the score report, the questions are broken down into 25 different subject areas, so there's likely a degree of overlap among them as well.