Subject: mathqa
Question: three pipes a , b and c can fill a tank from empty to full in 30 minutes , 20 minutes and 10 minutes respectively . when the tank is empty , all the three pipes are opened . a , b and c discharge chemical solutions p , q and r respectively . what is the proportion of solution q in the liquid in the tank after 3 minutes ?
Option: 
A: 2 / 11
B: 1 / 11
C: 3 / 11
D: 5 / 11
Answer: C