SOLUTION: Vernon, Joshua, and Dino are painting a house. Working together they can paint the house is 6 hours. Working alone Vernon can paint the house in 15 hours and Dino can paint the hou

The combined rate of work of the three workers is    of the job per hour.


The individual rates of the two participants are    and    of the job per hour.


Then the rate of work of the remained third participant is  the difference


     -  -  =  =  =   of the job per hour.


Hence, Joshua can complete the job in 20 hours, working alone.    ANSWER

    1)  You can solve this problem/(such problems) even without using equations.

        Freely manipulating fractions is enough.


    2)  Use the notion "rate of work" and remember:

            a)  when two or three persons work together, their combined rate of work is the sum of individual rates;


            b)  when the combined rate of three workers is given along with the individual rates of two of them, then the rate 
                of the third worker is the difference of combined rate and two given individual rates.