Arihant starts doing a certain piece of work. After 4 days, Arun, who is half as efficient as Arihant, joins him on the same work. As a result, the work gets completed in 9 more days. What is the total time required to complete the work if Arun does it entirely alone?

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?