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 Expiations P, Q and R respectively. What is the proportion of Expiation R in the liquid in the tank after 3 minutes?

5/11

6/11

7/11

8/11

Explanation:

Part filled by (A + B + C) in 3 minutes = 3(1/30 + 1/20 + 1/10) = 11/20.

Part filled by C in 3 minutes = 3/10

Hence, the Required ratio = 3/10 $\times$ 20/11 = 6/11.