$A$ can do a piece of work in $30 \text{ days}$ while $B$ can do it in $40 \text{ days}$. $A$ and $B$ working together can do it in (in $\text{days}$)

$A$ does a work in $10$ $days$ and $B$ does the same work in $15$ $days$. In how many $days$ will they together do the same work?

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

$A$ can finish a work in $24$ days,$B$ in $9$ days,and $C$ in $12$ days. $B$ and $C$ start the work but are forced to leave after $3$ days. The remaining work was done by $A$ in (in days):

$45$ men can complete a work in $16$ days. Four days after they started working,$36$ more men joined them. How many days will they now take to complete the remaining work?

$A$ and $B$ undertake a piece of work for $Rs. 250$. $A$ alone can do that work in $5$ days and $B$ alone can do that work in $15$ days. With the help of $C$,they finish the work in $3$ days. If everyone gets paid in proportion to the work done by them,the amount $C$ will get is (in $Rs.$)