$A$ certain number of persons can complete a piece of work in $55 \text{ days}$. If there were $6$ persons more,the work could be finished in $11 \text{ days}$ less. How many persons were originally there?

$4$ men and $6$ women earn $Rs. \, 1600$ by doing a piece of work in $5$ days. $3$ men and $7$ women earn $Rs. \, 1740$ by doing the same work in $6$ days. In how many days can $7$ men and $6$ women complete the same work while earning $Rs. \, 3760$?

$A$ and $B$ can do a piece of work in $12 \, \text{days}$ and $15 \, \text{days}$ respectively. They began to work together,but $A$ left after $4 \, \text{days}$. In how many more $days$ would $B$ alone complete the remaining work?

$A$ can do a work in $20 \, \text{days}$ and $B$ in $40 \, \text{days}$. If they work on it together for $5 \, \text{days}$, then the fraction of the work that is left is:

$A$ and $B$ can do a piece of work in $20$ days and $12$ days respectively. $A$ started the work alone and then after $4$ days $B$ joined him until the completion of the work. How long did the work last? (in days)

$P$,$Q$ and $R$ contracted to do a work for $Rs. 4200$. $P$ can do the work in $6$ days,$Q$ in $10$ days and $R$ in $12$ days. If they work together to do the work,what is the share of $R$ (in $Rs.$)?