Pipes A, B and C can fill a tank in 20, 30 and 60 hours, respectively. Pipes A, B and C are opened at 7 a.m., 8 a.m. and 9 a.m., respectively, on the same day. When will the tank be full?

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?

A. $$\frac{5}{{11}}$$

B. $$\frac{6}{{11}}$$

C. $$\frac{7}{{11}}$$

D. $$\frac{8}{{11}}$$

Pipes A and B can fill a tank in 5 and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in:

A. $$1\frac{{13}}{{17}}$$ hours

B. $$2\frac{8}{{11}}$$ hours

C. $$3\frac{9}{{17}}$$ hours

D. $$4\frac{1}{2}$$ hours

A pump can fill a tank with water in 2 hours. Because of a leak, it took $$2\frac{1}{3}$$ hours to fill the tank. The leak can drain all the water of the tank in:

A. $$4\frac{1}{3}$$ hours

B. 7 hours

C. 8 hours

D. 14 hours

Two pipes A and B can fill a cistern in $$37\frac{1}{2}$$ minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after:

A. 5 min.

B. 9 min.

C. 10 min.

D. 15 min.