An outlet pipe can empty a cistern in $3$ $h$. In what time (in $h$) will the pipe empty two-third part of the cistern?

$A$ 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?

One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in $36$ minutes,then the slower pipe alone will be able to fill the tank in (in minutes):

If pipe $P$ can fill a tank in $p$ hours and pipe $Q$ can empty the same tank in $q$ hours (where $q > p$),and both pipes are opened simultaneously,in how many hours $(r)$ will the tank be filled?

Three pipes $A, B$ and $C$ can fill a tank in $6$ $hours$. After running them together for $2$ $hours$, the tap $C$ is closed and $A$ and $B$ fill the remaining part in $7$ $hours$. How much time (in $hours$) would $C$ take to fill the tank alone?

Three pipes $A, B$ and $C$ can fill a tank in $6$ $hours$. After working together for $2$ $hours$,$C$ is closed and $A$ and $B$ fill the remaining part in $7$ $hours$. The number of $hours$ taken by $C$ alone to fill the tank is?