A, B and C are Accountants. A alone can file a return in 6 hours and B alone can file the same return in 10 hours. All three together can do it in 3 hours. In what time will C alone file the same return?

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?