Pipe $A$ can fill a tank in $4$ $hours$ and pipe $B$ can fill it in $6$ $hours$. If they are opened on alternate hours and if pipe $A$ is opened first,then in how many hours will the tank be full?

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?

$A$ pipe can empty a tank in $15$ $hrs$ and another pipe can empty it in $10$ $hrs$. If both the pipes are opened simultaneously, find the time in $hrs$ in which a full tank is emptied?

Three taps $A, B$ and $C$ fill a tank in $20$ min,$15$ min and $12$ min,respectively. If all the taps are opened simultaneously,how long will they take to fill $40 \%$ of the tank (in $min$)?

$A$ pipe $P$ can fill a tank in $12$ $min$ and another pipe $R$ can fill it in $15$ $min.$ But,the $3$rd pipe $M$ can empty it in $6$ $min.$ The $1$st two pipes $P$ and $R$ are kept open for $5$ $min$ in the beginning and then the $3$rd pipe is also opened. In what time (in minutes) is the tank emptied?

$A$ tank has two pipes. The first pipe can fill it in $45$ minutes and the second can empty it in $1$ hour. In what time will the empty tank be filled if the pipes are opened one at a time in alternate minutes?