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 pipes $A$,$B$,and $C$ can fill a cistern in $10$,$12$,and $15$ $hours$,respectively,while working alone. If all the three pipes are opened together,the time taken to fill the cistern will be:

Two pipes $A$ and $B$ can separately fill a cistern in $60$ $minutes$ and $75$ $minutes$ respectively. There is a third pipe in the bottom of the cistern to empty it. If all the three pipes are simultaneously opened,then the cistern is full in $50$ $minutes$. In how much time (in $minutes$) can the third pipe alone empty the cistern?

Two inlet pipes can fill a cistern in $10$ $hours$ and $12$ $hours$ respectively,and an outlet pipe can empty $80$ $gallons$ of water per hour. All three pipes working together can fill the empty cistern in $20$ $hours$. What is the capacity (in $gallons$) of the tank?

Two pipes can separately fill a tank in $20$ $hrs$ and $30$ $hrs$ respectively. Both the pipes are opened to fill the tank,but when the tank is $\frac{1}{3}$ full,a leak develops in the tank through which $\frac{1}{3}$ of the water supplied by both the pipes per hour leaks out. What is the total time (in $hrs$) taken to fill the tank?

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 $min$)?