If a job is to be completed in $10 \, \text{days}$,it requires $270 \, \text{persons}$. If $180 \, \text{persons}$ take up the same job,they will finish it 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?

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?

$A$ and $B$ working separately can do a piece of work in $9$ and $12$ days,respectively. If they work for a day alternately with $A$ beginning,the work would be completed in (in days):

$A, B$ and $C$ can do a piece of work in $30, 20$ and $10$ days respectively. $A$ is assisted by $B$ on one day and by $C$ on the next day,alternately. How long would the work take to finish? (in days)

$A, B$ and $C$ can complete a piece of work in $15, 30$ and $40$ days respectively. They started the work together,but $A$ left $2$ days before the completion of the work and $B$ left $4$ days before the completion of the work. In how many days was the work completed?