$15$ men take $20$ days to complete a job working $8$ hours a day. How many hours a day should $20$ men work to complete the same job in $12$ days?

$A$ and $B$ together can complete a work in $30$ days. They started together but after $6$ days $A$ left the work and the work is completed by $B$ after $36$ more days. $A$ alone can complete the entire work in how many days?

$P$ and $Q$ together can do a job in $6$ days. $Q$ and $R$ can finish the same job in $60/7$ days. $P$ started the work and worked for $3$ days. $Q$ and $R$ continued for $6$ days. Then the difference of days in which $R$ and $P$ can complete the job is

$12$ men and $16$ boys can do a piece of work in $5$ days. $13$ men and $24$ boys can do it in $4$ days. Then,the ratio of the daily work done by a man to that of a boy is:

$A$ is $50\%$ as efficient as $B$. $C$ does half of the work done by $A$ and $B$ together in the same time. If $C$ alone does the work in $20 \text{ days}$,then $A, B$,and $C$ together can do the work in (in $\text{days}$):

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