$A$ tap having diameter $d$ can empty a tank in $40$ $min$. How long will another tap having diameter $2d$ take to empty the same tank (in $min$)?

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?

$A$ tap takes $36$ hours extra to fill a tank due to a leakage equivalent to half of its inflow. In how many hours can the inlet pipe alone fill the tank?

$A$ 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 $min$)?

Three taps $A, B$ and $C$ can fill a tank in $12, 15$ and $20$ hours respectively. If $A$ is open all the time and $B$ and $C$ are open for one hour each alternately,the tank will be full in? (in hours)

$A$ 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?