Lindsay can paint 1/x of a certain room in 20 minutes. What fraction of the same room can Joseph paint in 20 minutes if the two of them can paint the room in an hour, working together at their respective rates?
Lindsay can paint 1/x of a certain room in 20 minutes
Lindsey and Joseph can paint 1/3 of room in 20 minuets.
so Joseph can paint the room 1/3 - 1/x in 20 minuets
so the fraction = (x - 3)/3x
+1 for the approach. Much faster and cleaner....good one gmat tiger.