Connie can wash nine windows in one hour. Rick can wash seven windows in one hour. Connie has been washing windows for one hour, when Rick joins her to finish the job. The entire job consists of washing 57 windows. How many hours does Rick work?
After one hour Connie has washed 9 of the 57 windows meaning 48 are left
Now when Rick joins in 9+ 7 windows get washed per hour = 16 windows /hour
48 windows / (16 windows/hr) = 3 hours to finish