A एक काम को 15 दिनों में पूरा कर सकता है और B उसी काम को 20 दिनों में पूरा कर सकता है। एक साथ काम करते हुए, वे उसी काम को कितने दिनों में पूरा कर सकते हैं?

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?