$A$ can do a work in $15 \text{ days}$ and $B$ in $20 \text{ days}$. If they work together on it for $4 \text{ days}$,then the fraction of the work that is left is

$A, B$ and $C$ individually can do a work in $10\, days, 12\, days$ and $15\, days,$ respectively. The number of days required to finish the work by $A, B$ and $C$ working together is? (in $days$)

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

$A$ and $B,$ working separately,can complete a piece of work in $9$ and $12$ days,respectively. If they work for a day alternately,$A$ beginning,in how many days will the work be completed?

$A$ can do a certain work in the same time in which $B$ and $C$ together can do it. If $A$ and $B$ together could do it in $10$ days and $C$ alone in $50$ days,then $B$ alone could do the work in (in days)

Akka can bake $100$ cakes in $20$ hours. Akka and Tai together can bake $75$ cakes in $10$ hours. How many cakes can Tai bake in $20$ hours?