How many $days$ will $1648$ persons take to construct a dam,if $721$ persons can build the same in $48$ days?

$A$ and $B$ can separately complete a piece of work in $20$ days and $30$ days respectively. They worked together for some time,then $B$ left the work. If $A$ completed the rest of the work in $10$ days,then for how many days did $B$ work?

If $12$ men or $18$ women can build a wall in $14$ days,then working at the same rate,$8$ men and $16$ women can build the same wall in how many days?

If $12$ men and $16$ boys can do a piece of work in $5 \, \text{days}$,and $13$ men and $24$ boys can do it in $4 \, \text{days}$,then the ratio of the daily work done by a man to that of a boy is:

$A$ can do a piece of work in $30$ days,$B$ in $50$ days,and $C$ in $40$ days. If $A$ is assisted by $B$ on one day and by $C$ on the next day alternately,the work will be completed in (in days):

$A$ can do $50\%$ of the job in $16$ days,$B$ can do $\frac{1}{4}^{th}$ of the job in $24$ days. In how many days can they do $\frac{3}{4}^{th}$ of the job working together?