Each inlet pipe can fill an empty cistern in 84 hours while each drain pipe can empty the same cistern from a filled condition in 105 hours. When the cistern is empty, 9 inlet pipes and 10 outlet pipes are simultaneously opened. After how many hours will the cistern be completely filled?

4 men’s work is equal to 6 women’s work, and 4 women’s work is equal to 6 boys’ work. A boy can finish the work in 60 days. In how many days can the work be finished by a man and a woman together?

A group of men decided to do a job in 11 days but 16 men left the work after each day. The work, as a result, got completed in 15 days. How many men were there initially in the group?