Pipe $A$ can fill a tank in $4$ $hours$ and pipe $B$ can fill it in $6$ $hours$. If they are opened on alternate hours and if pipe $A$ is opened first,then in how many hours will the tank be full?

Two pipes $A$ and $B$ together can fill a cistern in $4$ $hours$. Had they been opened separately,then $B$ would have taken $6$ $hours$ more than $A$ to fill the cistern. How much time (in $hours$) will be taken by $A$ to fill the cistern separately?

Three pipes $A, B$ and $C$ can fill a cistern in $6$ $hrs$. After working together for $2$ $hrs$,$C$ is closed and $A$ and $B$ fill the remaining part of the cistern in $8$ $hrs$. Find the time (in $hrs$) in which the cistern can be filled by pipe $C$ alone.

Two pipes $A$ and $B$ can fill a cistern in $24$ $minutes$ and $30$ $minutes$,respectively. There is also an outlet $C$. If all the three pipes are opened together,the cistern is full in $20$ $minutes$. How much time (in $minutes$) will be taken by outlet $C$ to empty the full cistern?

$A$ cistern has two pipes. One can fill it in $8 \, h$ and the other can empty it in $5 \, h$. In how many $hours$ will the cistern be emptied if both the pipes are opened together when $\frac{3}{4}$ of the cistern is already full of water?

$A$ pipe can fill a tank in $x$ $h$ and another pipe can empty it in $y$ $(y > x)$ $h.$ If both the pipes are open,in how many hours will the tank be filled?