$A$ and $B$ can separately do a piece of work in $6 \, \text{days}$ and $12 \, \text{days}$ respectively. How long will they together take to do the work? (in $\text{days}$)

$A$ can complete a work in $m$ days and $B$ can complete it in $n$ days. How many days will it take to complete the work if both $A$ and $B$ work together?

$3$ men and $2$ women can do a piece of work in $15$ days. $2$ men and $3$ women can do the same work in $18$ days. The number of days to be taken by $1$ man and $1$ woman to do the work is:

$A$ 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):

$A$ and $B$ can do a piece of work in $8$ days,$B$ and $C$ can do the same work in $12$ days,and $A, B,$ and $C$ together complete it in $6$ days. The number of days required to finish the work by $A$ and $C$ together is:

$4$ men and $6$ women together can complete a work in $8$ days,while $3$ men and $7$ women together can complete it in $10$ days. How many days will $20$ women working together take to complete the same work?