In a hostel, there was food provision for 300 students for 42 days. Due to examinations, some new students joined and the food lasted for only 36 days. How many new students joined the hostel?

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?