$A$ tank can be filled by pipe $A$ in $2$ $hours$ and pipe $B$ in $6$ $hours.$ At $10 \, am$ pipe $A$ was opened. At what time will the tank be filled if pipe $B$ is opened at $11 \, am$?

Two pipes $A$ and $B$ can fill a tank in $24$ $min.$ and $48$ $min.$ respectively. If both the pipes are opened simultaneously,after how much time (in $minutes$) $B$ should be closed so that the tank is full in $20$ $minutes$?

$A$ pipe can fill a tank in $10 \, h$, while another pipe can empty it in $6 \, h$. Find the time (in $hours$) taken to empty the tank when both the pipes are opened simultaneously.

Pipe $A$ can fill a cistern in $6 \, h$ and pipe $B$ can fill it in $8 \, h$. Both the pipes are opened simultaneously,but after $2 \, h$ pipe $A$ is closed. How many hours will $B$ take to fill the remaining part of the cistern?

An oil drum can be filled with oil in $40$ $min$ by a filling pipe. Another outlet pipe can empty the entire drum in $60$ $min$. The outlet pipe was opened when $\frac{2}{3}$ part of the drum was filled with oil and closed after $15$ $min$. What time will it take to fill the drum when the filling pipe is opened now?

$A$ reservoir is fitted with two pipes $A$ and $B$. Pipe $A$ can fill the reservoir $5$ $hours$ faster than pipe $B$. If both the pipes together fill the reservoir in $6$ $hours$,the reservoir will be filled by $A$ alone in: