After working together for 2 days to complete a piece of work, P and Q received Rs. 1200 and Rs. 400 respectively as wages. In how many days can Q alone complete the entire work?

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?