$A$ 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?

$A$ tap can fill a cistern in $40$ $min$ and a second tap can empty the filled cistern in $60$ $min$. By mistake, without closing the second tap, the first tap was opened. In how many $minutes$ will the empty cistern be filled?

$A$ tap can fill a cistern in $8$ $hours$ and another can empty it in $16$ $hours$. If both the taps are opened simultaneously,the time (in $hours$) to fill the tank is?

Two taps $P$ and $Q$ can fill a water tank in $12$ $min$ and $15$ $min$ respectively. They are opened together,but after $3$ $min$,tap $P$ is closed. How much more time will $Q$ take to fill the remaining part of the tank?

Two taps $A$ and $B$ can fill a tank in $20 \text{ min}$ and $30 \text{ min}$,respectively. An outlet pipe $C$ can empty the full tank in $15 \text{ min}$. If $A, B$,and $C$ are opened alternatively,each for $1 \text{ min}$,how long (in $\text{min}$) will the tank take to be filled?

Two taps $A$ and $B$ can fill a tank in $10$ $hours$ and $15$ $hours$,respectively. If both the taps are opened together,the tank will be full in (in $hours$):