$A$ 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?

Two pipes $A$ and $B$ can fill a cistern in $4$ $minutes$ and $6$ $minutes,$ respectively. If these pipes are turned on alternately for $1$ $minute$ each,then how long will it take for the cistern to fill?

Two pipes can fill a cistern separately in $24$ $minutes$ and $40$ $minutes$ respectively. $A$ waste pipe can drain off $30 \text{ litres per minute}$. If all the three pipes are opened,the cistern fills in one $hour$. The capacity (in $litres$) of the cistern is:

An inlet pipe fills $\frac{1}{8}$ part of a tank in $1 \ h$. How much time (in $h$) will the pipe take to fill the empty tank?

Two taps $A$ and $B$ can fill a water tank in $20$ $min$ and $24$ $min$ respectively,and a third tap $C$ empties the tank at a rate of $3$ $gallons$ per $min$. If all three taps $A$,$B$,and $C$ are opened together,the tank is filled in $15$ $min$. What is the capacity of the tank in $gallons$?

Two pipes $A$ and $B$ can fill a tank in $15$ minutes and $20$ minutes respectively. Both the pipes are opened together but after $4$ minutes,pipe $A$ is turned off. What is the total time required to fill the tank?