$A$ and $B$ together can complete a piece of work in $12$ days and $B$ and $C$ together in $15$ days. If $A$ is twice as good a workman as $C$,then in how many days will $B$ alone complete the same work?

$A$ and $B$ can do a job in $6$ and $12$ days,respectively. They began the work together,but $A$ leaves after $3$ days. Then,the total number of days needed for the completion of the work is:

$A$ does half as much work as $B$ in $\frac{3}{4}$ of the time. If together they take $18$ days to complete a work,then how much time shall $B$ take to complete it? (in days)

$A$ takes twice as much time as $B$ and $C$ takes thrice as much time as $B$ to finish a piece of work. Working together they can finish the work in $12$ days. The number of days needed for $A$ to do the work alone is:

$P, Q$ and $R$ can finish a work in $10, 12$ and $15$ days respectively. If $Q$ stops after $2$ days,how long would it take $P$ and $R$ to finish the remaining work? (in days)

$A$ and $B$ can do a piece of work in $30$ days,while $B$ and $C$ can do the same work in $24$ days and $C$ and $A$ in $20$ days. They all work together for $10$ days when $B$ and $C$ leave. How many days more will $A$ take to finish the work?