10 men can complete a piece of work in 15 days and 15 women can complete the same work in 12 days. If all 10 men and 15 women work together, in how many days will the work be completed?

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?