Sally can paint a room in 7 hours while it takes Steve 6 hours to paint the same room. How long would it take them to paint the room if they worked together.

Sally paints at a rate of 1/7th room / hour

Steve paints at a rate of 1/6th room / hour

If they both painted together, they would paint 1/7 + 1/6 = 13/42 room/hour

so to paint the whole room, it would take 1 / (13/42) = 42/13 =

3.23 hours (3 significant figures)