Shashi can do a piece of work in $20$ days. Tanya is $25\%$ more efficient than Shashi. The number of days taken by Tanya to do the same piece of work is

$A, B$ and $C$ can do a piece of work individually in $8, 10$ and $15$ days respectively. $A$ and $B$ start working,but $A$ quits after working for $2$ days. After this,$C$ joins $B$ until the completion of the work. In how many days will the work be completed?

$A$ can do a piece of work in $14$ days,which $B$ can do in $21$ days. They begin together,but $3$ days before the completion of the work,$A$ leaves. The total number of days to complete the work is:

$A$ and $B$ can complete a piece of work in $30 \text{ days}$,$B$ and $C$ in $40 \text{ days}$,while $C$ and $A$ in $60 \text{ days}$. $A, B, C$ together can complete the work in (in $\text{days}$):

$A$ does half as much work as $B$ in $three-fourths$ of the time. If together they take $18$ days to complete a work,how much time shall $B$ take to do it alone? (in days)

$A$ can do a piece of work in $30$ days,$B$ in $50$ days,and $C$ in $40$ days. If $A$ is assisted by $B$ on one day and by $C$ on the next day alternately,the work will be completed in (in days):