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

26. A can do a piece of work in 24 days while B alone can do it in 16 days. With the help of C, they finish the work in 8 days. C alone can do the work in:

27. 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 off. The total number of days to complete the work is: