$P, Q$ 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)

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?

$A$ 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):

$A$ man can do a piece of work in $5$ days,but with the help of his son,he can do it in $3$ days. In what time can the son do it alone? (in 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?

$A$ certain number of men can do a piece of work in $40 \, days$. If there were $45 \, men$ more,the work could have been finished in $25 \, days$. Find the original number of men employed in the work.