Scheme of Abbreviation
P: Monica is sleeping with Chandler
Q: Rachel is sleeping with Ross
R: Rachel knows
S: Joey knows
T: Phoebe knows
V: Ross knows

1. Though Monica is sleeping with Chandler, neither Ross nor Phoebe knows.
 
2. Monica is sleeping with Chandler, but Rachel, who is not sleeping with Ross, does not know.
 
3. Both Rachel and Joey know, but neither Ross nor Phoebe does.
 
4. It’s not true that both Rachel and Ross know.
 
5. Ross and Phoebe both do not know.
 
6. If Rachel knows only if Ross knows, and Joey knows only if Phoebe knows, then neither Rachel nor Joey knows.
 
7. Either Monica is sleeping with Chandler or Rachel is sleeping with Ross, but not both.
 
8. If Ross knows only if Phoebe knows, then Ross does not know.
 
9. Assuming that Ross knows if Rachel knows, then they both know given that Phoebe knows.
 
10. Rachel knows, but that is not sufficient for Phoebe to know.