If a pipe fills a tank in $6 \ h$,then what part of the tank will the pipe fill in $1 \ h$?

$A$ pipe can fill a cistern in $4$ $min$ and another pipe can fill it in $5$ $min,$ but a third pipe can empty it in $2$ $min.$ The first two pipes are kept open for $2$ $min$ in the beginning and then the third pipe is also opened. Time (in $min$) taken to empty the cistern is?

Two pipes $A$ and $B$ can separately empty a cistern in $12$ $hours$ and $15$ $hours$,respectively. In what time will the cistern be emptied,if both the pipes are opened together?

Three taps $A, B$ and $C$ can fill a tank in $12, 15$ and $20$ hours respectively. If $A$ is kept open all the time,and $B$ and $C$ are opened for one hour each alternately,how long will it take to fill the tank?

If two pipes function simultaneously,the reservoir will be filled in $6$ $hours$. One pipe fills the reservoir $5$ $hours$ faster than the other. How many $hours$ does the faster pipe take to fill the reservoir?

$A$ tap drips at a rate of $1$ drop/sec. If $600$ drops make $100 \text{ ml}$,the number of litres wasted in $300$ days is: