$A$ is $20\%$ more efficient than $B$. If $B$ alone can complete a piece of work in $12$ days,then $A$ alone can complete the same work in how many days?

$A$ can do a piece of work in $30$ days while $B$ can do it in $40$ days. In how many days can $A$ and $B$ working together do it?

$A$ takes $10\, \text{days}$ less than the time taken by $B$ to finish a piece of work. If both $A$ and $B$ can do it in $12\, \text{days}$, then the time taken by $B$ alone to finish the work is (in $\text{days}$)

$12$ men complete a work in $9$ days. After they have worked for $6$ days,$6$ more men join them. How many days will they take to complete the remaining work?

$A$ and $B$ can do a piece of work in $12$ days, $B$ and $C$ in $8$ days, and $C$ and $A$ in $6$ days. How long would $B$ take to do the same work alone? (in days)

$A, B$ and $C$ can do a piece of work in $30, 20$ and $10$ days respectively. $A$ is assisted by $B$ on one day and by $C$ on the next day,alternately. How long would the work take to finish? (in days)