Two pipes, A and B, can fill a tank in 60 hours and 90 hours, respectively. If both the pipes are opened simultaneously, in how many hours will 75% of the tank be filled?

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?