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 five hours, what fraction of the room can Joseph paint in 20 minutes?
Choose the correct choice from the following
A) 1/5x B) x/(x-3) C) (x-5)/15x D) x/(x-5) E) (x-5)/x
Let J be Joseph's rate per hour.   1/x + J = 1/5 of a room per hour   J = 1/5 - 1/x, of a room per hour   In 20 minutes, Joseph can paint 1/3*(1/5-1/x) = 1/15-1/3x = (x-5)/15x   The answer is (x-5)/15x.
<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 five hours, what fraction of the room can Joseph paint in 20 minutes?