$A$ 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 $min$)?

Two taps can fill a tank in $20$ $min$ and $30$ $min$ respectively. When the tank was empty,both the taps were opened,and after some time,the first tap was closed. It took $18$ $min$ in total to fill the tank. After how much time (in $minutes$) from the beginning was the first tap closed?

Having the same capacity,$9$ taps fill up a water tank in $20$ minutes. How many taps of the same capacity are required to fill up the same water tank in $15$ minutes?

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?

$A$ 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 can fill a tank in $20$ and $24$ $minutes$ respectively and a waste pipe can empty $3$ $gallons$ per $minute$. All the three pipes working together can fill the tank in $15$ $minutes$. The capacity of the tank is?