SOLUTION: Elvis can plough a field in 30 days. Mark can do it in 24 days and Peter in 20 days. How long will take Peter to finish it by himself if starts when Elvis and Mark have each done 6

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Elvis can plough a field in 30 days. Mark can do it in 24 days and Peter in 20 days. How long will take Peter to finish it by himself if starts when Elvis and Mark have each done 6      Log On


   

Question 872324: Elvis can plough a field in 30 days. Mark can do it in 24 days and Peter in 20 days. How long will take Peter to finish it by himself if starts when Elvis and Mark have each done 6 days work?
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
"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: How long will take Peter to finish it by himself if starts when Elvis and Mark have each done 6 days work?

Answer: 11 days