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?

If $3$ men and $4$ boys can earn $Rs. 2100$ in $7$ days,and $11$ men and $13$ boys can earn $Rs. 8300$ in $8$ days,in what time will $7$ men and $9$ boys earn $Rs. 11000$? (in days)

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

$A$ and $B$ can do a piece of work in $12$ days and $15$ days,respectively. They began to work together,but $A$ left after $4$ days. In how many more days would $B$ alone complete the remaining work?

$12$ 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?

$A$ is twice as good a workman as $B$. Working together,they finish a piece of work in $1.5$ days. $A$ alone can finish the work in (in days):