10. A does half as much work as B in three-fourth of the time. If together they take 18 days to complete a work, how much time shall B talk to do it?

11. A is thrice as good a workman as B and takes 10 days less to do a piece of work than B takes. B can do the work in:

12. A and B can do a piece of work in 18 days; B can C in 24 days; A and C in 36 days. In what time can they do it all working together?