If $8$ men or $10$ women can do a piece of work in $50$ days,in what time will $28$ men and $15$ women do it? (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)

$A$ 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 $\text{days}$):

$7$ men can complete a piece of work in $12$ days. How many additional men will be required to complete double the work in $8$ 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?

Three men,four women and six children can complete a work in $7$ days. $A$ woman does double the work a man does and a child does half the work a man does. How many women alone can complete this work in $7$ days?