Pipe $X$ can fill a tank in $20$ $hours$ and pipe $Y$ can fill the tank in $35$ $hours.$ Both the pipes are opened on alternate hours. Pipe $Y$ is opened first,then in how much time (in hours) will the tank be full?

$A$ 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?

$A$ leak in the bottom of a tank can empty the full tank in $8$ $hours$. An inlet pipe fills water at the rate of $6$ $litres$ a minute. When the tank is full,the inlet pipe is opened and due to the leak,the tank is empty in $12$ $hours$. How many litres does the tank hold?

$A$ water tank has two pipes. The empty tank is filled in $12$ $min$ by the $1$st pipe and the full tank is emptied by the $2$nd pipe in $20$ $min$. What is the time required to fill the $1/2$ full tank when both pipes are in action (in $min$)?

Pipe $A$ can fill an empty tank in $6$ $hours$ and pipe $B$ in $8$ $hours$. If both the pipes are opened and after $2$ $hours$ pipe $A$ is closed,how much time will pipe $B$ take to fill the remaining tank?

$A$ pipe $P$ can fill a tank in $12$ $min$ and another pipe $R$ can fill it in $15$ $min.$ But,the $3$rd pipe $M$ can empty it in $6$ $min.$ The $1$st two pipes $P$ and $R$ are kept open for $5$ $min$ in the beginning and then the $3$rd pipe is also opened. In what time (in minutes) is the tank emptied?