Question

Sally paints a room in 6 hours while it takes Steve 9 hours to paint the same room. how long would it take them to paint the room if they worked together

Answer 1

If Sally paints one room per six hours, she paints 1/6 of the room every hour.  Similarly, Steve paints 1/9 of the room every hour.  Therefore, together, they paint 1/6+1/9=5/18 of the room every hour.  Therefore, it takes the 18/5 of an hour to paint the whole room, since 18/5*5/18=1, so 18/5 of an hour at 5/18 of the room per hour is one room.