Having the same capacity,$9$ taps fill up a water tank in $20$ minutes. How many taps of the same capacity are required to fill up the same water tank in $15$ minutes?

Two pipes,$A$ and $B,$ can separately fill a tank in $6$ $hours$ and $8$ $hours,$ respectively. Both the pipes are opened together,but $1 \frac{1}{2}$ $hours$ later pipe $A$ is turned off. How much time (in $hours$) will it take to fill the tank?

$A$ water tank is $\frac{2}{5}$ full. Pipe $A$ can fill the tank in $10$ $minutes$ and pipe $B$ can empty it in $6$ $minutes$. If both the pipes are open,then how long will it take to empty or fill the tank completely?

$A$ tank can be filled by pipe $A$ in $2$ $h$ and pipe $B$ in $6$ $h$. At $10$ $am$ pipe $A$ was opened. At what time will the tank be filled if pipe $B$ is opened at $11$ $am$?

$A$ pipe can fill a cistern in $4$ $min$ and another pipe can fill it in $5$ $min,$ but a third pipe can empty it in $2$ $min.$ The first two pipes are kept open for $2$ $min$ in the beginning and then the third pipe is also opened. Time (in $min$) taken to empty the cistern is?

$A$ swimming pool has $3$ drain pipes. The first two pipes $A$ and $B$,operating simultaneously,can empty the pool in half the time that $C$ (the $3rd$ pipe) alone takes to empty it. Pipe $A$,working alone,takes half the time taken by pipe $B$. Together they take $6$ $hours$ $40$ $minutes$ to empty the pool. Time taken by pipe $A$ to empty the pool,in hours,is