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 R in the liquid in the tank after 3 minutes? Choose the correct choice:
A) 6/19
B) 6/11
C) 6/12
D) 6/10
E) 6/38
Part filled by (A + 6/11 + C) in 3 minutes = 3(1/30 + 1/20 + 1/10) = 11/20   Part filled by C in 3 minutes = 3/10   Required ratio = 3/10 * 20/11 = 6/11   Answer:6/11
<result>B</result>
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 R in the liquid in the tank after 3 minutes?