If a work can be completed by $A$ in $30 \text{ days}$ and by $B$ in $60 \text{ days}$,then the number of days taken by them to finish the work,working together,is

$A$ can finish a work in $12$ days and $B$ can do it in $15$ days. After $A$ had worked for $3$ days,$B$ also joined $A$ to finish the remaining work. In how many days will the remaining work be finished?

Bindal can finish a work in $10$ days. Jindal is twice as efficient as Bindal. If they work together,in how many days will the work be completed?

$A$ and $B$ can together finish a work in $30$ days. They worked at it for $20$ days and then $B$ left. The remaining work was done by $A$ alone in $20$ more days. $A$ alone can finish the work in (in days):

$A$ and $B$ together can do a piece of work in $10$ days. $A$ alone can do it in $30$ days. The time in which $B$ alone can do it is (in days):

$A$ can finish a work in $24$ days,$B$ in $9$ days and $C$ in $12$ days. $B$ and $C$ start the work but are forced to leave after $3$ days. The remaining work was done by $A$ in (in days):