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?

$A, B, C$ are pipes attached to a cistern. $A$ and $B$ can fill it in $20$ and $30$ minutes respectively,while $C$ can empty it in $15$ minutes. If $A, B, C$ are kept open successively for $1$ minute each,how soon will the cistern be filled? (in minutes)

Three taps $P, Q$ and $R$ separately can fill a tank completely in $4, 8$ and $12$ hours respectively. Another tap $S$ can empty the filled tank in $10$ hours. Which of the following combinations will fill the empty tank in the least amount of time?

Three pipes $A$,$B$,and $C$ can fill a cistern in $10$,$12$,and $15$ $hours$,respectively,while working alone. If all the three pipes are opened together,the time taken to fill the cistern will be:

There are two taps to fill a tank while a third tap is used to empty it. When the third tap is closed,the first two taps can fill the tank in $10$ $minutes$ and $12$ $minutes$ respectively. If all three taps are opened,the tank is filled in $15$ $minutes$. If the first two taps are closed,in what time can the third tap empty the tank when it is full?

An oil drum can be filled with oil in $40$ $min$ by a filling pipe. Another outlet pipe can empty the entire drum in $60$ $min$. The outlet pipe was opened when $\frac{2}{3}$ part of the drum was filled with oil and closed after $15$ $min$. What time will it take to fill the drum when the filling pipe is opened now?