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

How many men will be required to plough $100 \, acres$ of land in $10 \, days$ if $10 \, men$ require $8 \, days$ to plough $20 \, acres$ of land?

$A, B$ and $C$ together can finish a piece of work in $4$ days. $A$ alone can do it in $12$ days and $B$ alone in $18$ days. How many days will be taken by $C$ to do it alone?

$A, B$ and $C$ can complete a piece of work in $6, 12$ and $24$ days respectively. They altogether will complete the work in (in days):

$10$ men and $15$ women together can complete a work in $6$ days. It takes $100$ days for one man alone to complete the same work. How many days will be required for one woman alone to complete the same work?

$A$ contractor has the target of completing a work in $40 \text{ days}$. He employed $20$ persons who completed $\frac{1}{4}$ of the work in $10 \text{ days}$ and left. The number of additional persons he has to employ to finish the remaining part of the work as per the target is: