$A$ 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)

Two workers $A$ and $B$ working together completed a job in $5$ days. If $A$ worked twice as efficiently as he actually did and $B$ worked $\frac{1}{3}$ as efficiently as he actually did,the work would have completed in $3$ days. Find the time for $A$ to complete the job alone (in days).

If $28$ men complete $\frac{7}{8}$ of a piece of work in a week,then the number of men,who must be engaged to get the remaining work completed in another week is

$A$ can do a piece of work in $24$ days,$B$ in $32$ days,and $C$ in $64$ days. All begin to do it together,but $A$ leaves $6$ days before the completion of the work. How many days did the work last?

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)

$A, B$ and $C$ together can complete a piece of work in $30\, min$. $A$ and $B$ together can complete the same work in $50\, min$. $C$ alone can complete the work in? (in $min$)