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 the solution R in the liquid in the tank after 3 minutes?
Answer: B
Part filled by (A + B + C) in 3 minutes = 3 (1/30 + 1/20 + 1/10) = (3 × 1/60) = 11/20
Part filled by C in 3 minutes = 3/10 .
Required ratio = (3/10 ×: 20/11) = 6/11