Laura can paint 1/x of a certain room in 20 minutes. What fraction W 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?  Pick one:
A) 1/(3x)  B) 3x/(x-3)  C) (x – 3)/(3x)  D) x/(x-3)  E) (x-3)/x
Options with variables are often done by plugging in numbers.   Both working together can paint the room in 1 hr so if their individual rates were equal, each would take 2 hours alone.   2 hours is 120 mins so in 20 mins each would complete W=120/20 = 1/6th of the room alone.   So if x = 6 (Laura completes 1/6th of the room in 20 mins), the correct option will give 1/6. (Joseph will also paint 1/6th of the room if their rates are same)   If you put x = 6 in the options, only option ((x – 3)/(3x)) will give 1/6   Answer ((x – 3)/(3x))
<result>C</result>
Laura can paint 1/x of a certain room in 20 minutes. What fraction W 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?