Two pipes $A$ and $B$ can fill a cistern in $3$ $hours$ and $5$ $hours,$ respectively. Pipe $C$ can empty it in $2$ $hours.$ If all the three pipes are open,in how many $hours$ will the cistern be full?

Three pipes $A, B$ and $C$ can fill a cistern in $10$ $hours$,$12$ $hours$ and $15$ $hours$ respectively. First $A$ was opened. After $1$ $hour$,$B$ was opened and after $2$ $hours$ from the start of $A$,$C$ was also opened. Find the time in which the cistern is just 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?

$A$ water tank is $\frac{2}{5}$ full. Pipe $A$ can fill the tank in $10$ $minutes$ and pipe $B$ can empty it in $6$ $minutes$. If both the pipes are open,then how long will it take to empty or fill the tank completely?

Two taps $A$ and $B$ can fill a tank in $25$ $min$ and $20$ $min$ respectively. However,the taps are not opened properly,so taps $A$ and $B$ allow only $\frac{5}{6}$ and $\frac{2}{3}$ of their normal water flow,respectively. How long will they take to fill the tank (in $min$)?

$A$ boy and a girl together fill a cistern with water. The boy pours $4$ litres of water every $3$ minutes and the girl pours $3$ litres every $4$ minutes. How much time (in minutes) will it take to fill $100$ litres of water in the cistern?