Question 801748
Examine the rates of each worker.  You have one slow worker and two fast workers.  The slow worker needs 2d days to do one job, so {{{1/(2d)}}} is this slow worker rate.  The fast workers each could do one job in d days, so each of his rate is {{{1/d}}} job per day.  The three workers acting together have the rate {{{1/12}}} jobs per day.


Using the original description, first sentence, and the rate expressions of the three workers, formulate the equation for these three workers when acting together:


{{{highlight(1/(2d)+1/d+1/d=1/12)}}} since each rate adds simply.  Solve for d.  This will be how many days working alone one fast worker can do this 1 job.