Lindsay can paint 1/x of a certain room in one hour. If Lindsay and Joseph, working together at their respective rates, can paint the room in four hours, what fraction of the room can Joseph paint in 20 minutes?	Choose one
A) 1/4x  B) x/(x-12)  C) (x-4)/12x  D) x/(x-4)  E) (x-4)/x
Let J be Joseph's rate per hour.   1/x + J = 1/4 of a room per hour   J = 1/4 - 1/x, of a room per hour   In 20 minutes, Joseph can paint 1/3*(1/4-1/x) = 1/12-1/3x = (x-4)/12x   The answer is (x-4)/12x.
<result>C</result>
Lindsay can paint 1/x of a certain room in one hour. If Lindsay and Joseph, working together at their respective rates, can paint the room in four hours, what fraction of the room can Joseph paint in 20 minutes?