Pipe $X$ can fill a tank in $20$ $hours$ and pipe $Y$ can fill the tank in $35$ $hours.$ Both the pipes are opened on alternate hours. Pipe $Y$ is opened first,then in how much time (in hours) will the tank be full?

$A$ tank can be filled with water by two pipes $A$ and $B$ together in $36$ minutes. If the pipe $B$ was closed after $30$ minutes,the tank is filled in $40$ minutes. The pipe $B$ can alone fill the tank in?

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 $min$)?

$A$ cistern is normally filled in $8$ $hours$,but it takes $2$ $hours$ longer to fill because of a leak at its bottom. If the cistern is full,the leak will empty it in (in $hours$):

Two pipes $A$ and $B$ can fill a tank in $24$ $minutes$ and $32$ $minutes$ respectively. If both the pipes are opened simultaneously,after how much time (in $minutes$) should $B$ be closed so that the tank is full in $18$ $minutes$?

Two taps $A$ and $B$ can fill an oil tank in $15$ $min$ and $18$ $min$ respectively,while a third tap is used to empty the tank. The third tap is opened after $6$ $min$ of opening of taps $A$ and $B$. If the tank empties in $16 \frac{1}{2}$ $min$ after opening the third tap,then in how much time (in $min$) can the third tap empty the full tank?