$A$ pipe can empty a tank in $15$ $hrs$ and another pipe can empty it in $10$ $hrs$. If both the pipes are opened simultaneously, find the time in $hrs$ in which a full tank is emptied?

Three pipes $A$,$B$,and $C$ can fill a cistern in $10$,$12$,and $15$ $hours$,respectively,while working alone. If all the three pipes are opened together,the time taken to fill the cistern will be:

$A$ pipe can fill a tank with thrice the speed of another pipe. If both the pipes together take $36$ $min$ to fill an empty tank completely,then how much time will it take for the slower pipe to fill the tank alone?

$A$ tank has a leak which would empty it in $8$ $hrs$. $A$ tap is turned on which admits $6$ $litres$ a minute into the tank,and it is now emptied in $12$ $hrs$. How many litres does the tank hold?

Three taps are fitted in a cistern. The empty cistern is filled by the first and the second taps in $3 \, h$ and $4 \, h$, respectively. The full cistern is emptied by the third tap in $5 \, h$. If all three taps are opened simultaneously, the empty cistern will be filled up in?

Pipes $P$ and $Q$ can fill a tank in $10$ and $12$ $h$, respectively, and pipe $C$ can empty it in $6$ $h$. If all the three are opened at $7$ $am$, at what time will one-fourth of the tank be filled?