Question 872324
"Elvis can plow a field in 30 days.", so he does 6/30 = 1/5 of the job done in 6 days.


"Mark can do it in 24 days", so he does 6/24 = 1/4 of the job done in 6 days.


Put together, they get 1/5 + 1/4 = 4/20 + 5/20 = 9/20 of the job done after 6 days have gone by.


There is 1 - 9/20 = 20/20 - 9/20 = 11/20 of the job left to be done.


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Peter can do the job in 20 days, so his rate is 1/20 of a job per day.


(1 job/20 days)*(x days) = 11/20 job


x/20 = 11/20 


20x = 11*20


20x = 220


x = 220/20


x = 11


Question: <font color="blue">How long will take Peter to finish it by himself if starts when Elvis and Mark have each done 6 days work?  </font>


Answer: <font color="red">11 days</font>