Working together, A and B finish a job 1 day faster than B alone. When working at half of his efficiency, B finishes the job alone in 10 days. Find the ratio of the efficiency of A to that of B.

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?