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

$A$ certain job was assigned to a group of men to do in $20$ days. But,$12$ men did not turn up for the job and the remaining men did the job in $32$ days. The original number of men in the group was:

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?

Four examiners can examine a certain number of answer papers in $10$ days by working for $5$ hours a day. For how many hours in a day would $2$ examiners have to work in order to examine twice the number of answer papers in $20$ days?

$A$ can do a piece of work in $15 \text{ days}$. With the help of $A$,$B$ can do it in $6 \frac{2}{3} \text{ days}$. $B$ can do it alone in (in $\text{days}$)

$A$ can do $\frac{1}{3}$ of a work in $5 \text{ days}$ and $B$ can do $\frac{2}{5}$ of the work in $10 \text{ days}$. In how many $\text{days}$ can both $A$ and $B$ together do the work?