$A$ tank can be filled by one tap in $20$ $minutes$ and by another in $25$ $minutes$. Both the taps are kept open for $5$ $minutes$ and then the second is turned off. In how many $minutes$ more will the tank be completely filled?

Two pipes $A$ and $B$ can fill a tank in $15$ hours and $20$ hours respectively,while a third pipe $C$ can empty the full tank in $25$ hours. All three pipes are opened in the beginning. After $10$ hours,pipe $C$ is closed. Find the total time (in hours) in which the tank will be full.

$A$ tap can fill a tank in $6$ $h$. After half the tank is filled,three more similar taps are opened. What is the total time taken to fill the tank completely?

Pipes $P$ and $Q$ can fill a tank in $5$ and $6 \, h$, respectively, and pipe $C$ can empty it in $3 \, h$. If all the three are opened at $7 \, am$, at what time will two-fifths of the tank be filled?

$18$ pumps can fill a reservoir of capacity $1440 \text{ kilo liter}$ in $5 \text{ hours}$. How many $\text{hours}$ are required to fill a reservoir of capacity $1920 \text{ kilo liter}$ by $8$ pumps?

Two pipes $A$ and $B$ can fill a tank in $30$ $minutes$ and $45$ $minutes$ respectively. Pipe $C$ can empty the tank in $36$ $minutes$. Initially,pipes $A$ and $B$ are opened. After $12$ $minutes$,pipe $C$ is also opened. What is the total time (in $minutes$) required to fill the tank?