Pipe A can fill an empty cistern alone in 13 hours and pipe B can fill the same cistern alone in 20 hours. The time taken by them to fill half of the cistern by operating together will be:

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?