11.

An electric pump can fill a tank in $3$ hours. Because of a leak in the tank, it took $3\frac{1}{2}$ hours to fill the tank. If the tank is full, how much time will the leak take to empty it ?

A) 21 hours

B) 20 hours

C) 30 hours

D) 40 hours

E) 50 hours

12.

A cistern has two taps which fill it in $12$ minutes and $15$ minutes respectively. There is also a waste pipe in the cistern. When all the three are opened, the empty cistern is full in $20$ minutes. How long will the waste pipe take to empty the full cistern ?

A) 20 minutes

B) 30 minutes

C) 40 minutes

D) 50 minutes

E) 10 minutes

13.

Two pipes can fill a tank in $10$ hours and $12$ hours respectively while a third pipe empties the full tank in $20$ hours. If all the three pipes operate simultaneously, in how much time will the tank be filled ?

A) 7 hrs 30 min

B) 7 hrs 40 min

C) 7 hrs 50 min

D) 8 hrs 30 min

E) 7 hrs

14.

Two pipes C and D can fill a tank in 36 hours and 45 hours respectively. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?

A) 40 hours

B) 50 hours

C) 60 hours

D) 20 hours

E) none of the above

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