An inlet pipe fills $\frac{1}{8}$ part of a tank in $1 \ h$. How much time (in $h$) will the pipe take to fill the empty tank?

Two pipes $A$ and $B$ can separately fill a cistern in $60$ $minutes$ and $75$ $minutes$ respectively. There is a third pipe in the bottom of the cistern to empty it. If all the three pipes are simultaneously opened,then the cistern is full in $50$ $minutes$. In how much time (in $minutes$) can the third pipe alone empty the cistern?

Pipes $P$ and $Q$ can fill a tank in $10$ and $12$ $h$, respectively, and pipe $C$ can empty it in $6$ $h$. If all the three are opened at $7$ $am$, at what time will one-fourth of the tank be filled?

Two pipes can fill a tank in $15$ $hours$ and $12$ $hours$ respectively,while a third pipe can empty it in $20$ $hours$. If the tank is empty and all three pipes are opened together,then in how much time will it take to fill the tank completely?

$A$ tap can fill a tank in $25$ $minutes$ and another can empty it in $50$ $minutes$. Find out whether the tank will be filled up or emptied and in how many $minutes$?

$A$ cistern has two taps which fill it in $12$ $minutes$ and $15$ $minutes,$ respectively. There is also a waste pipe in the cistern. When all the pipes are opened, the empty cistern is full in $20$ $minutes.$ How long will the waste pipe take to empty a full cistern?