C1, C2 and C3 can do a work alone in 10, 12 and 15 days respectively. All three of them began the work together but C2 left 2 days before the completion of the work. In how many days was the work complete d?

If P and Q together can complete a piece of work in 15 days and P alone can do it in 45 days, in how many days can Q alone complete that work?

A can lay a railway track between two stations in 16 days and B can do the same job in 12 days. With the help of C, they finished the job in 4 days. In how many days can C alone do the job?